Lamb Moussaka

Allow 20 minutes to check the equipment and fridge space, dice the onion, chop the garlic and measure the filling ingredients and seasonings. Keep the mince refrigerated until it goes into the pan. Check use-by and storage instructions. If you have bought a 1kg pack, separate the 500g needed here while it is cold; refrigerate the remainder promptly or freeze according to its label. Keep raw meat and its utensils away from the containers for cooked food, then wash hands and clean raw-contact surfaces. This is a two-session recipe: the filling and aubergine will be cooled promptly, refrigerated and used the following day, not left out while the other components are made. The baseline schedule is 3 hours 34 minutes for this first session, a planned 12-hour fridge interval after the last load is refrigerated, then 2 hours 5 minutes for the second session: 17 hours 39 minutes overall. Allow longer for extra loads or slower cooking and cooling.

Warm 15ml of the oil in the sauté pan over medium heat for 2 minutes. Add the onion and cook for about 8 minutes, stirring until softened. Stir in the garlic for 1 minute. Add all 500g mince, raise the heat to medium-high and break it into small pieces with the spoon. Cook for about 12 minutes, stirring and allowing released moisture to evaporate until there are browned patches and no large clumps. The onion remains in the pan; there is no bowl of partly cooked meat waiting between batches. If a pool of fat remains, take the pan off the heat and spoon the excess into a heatproof waste container, leaving a light film; allow for this handling within the mince stage. Do not pour hot fat down the sink. Set raw-contact tools aside for washing and use a clean spoon for the finished sauce.

Lower the heat to medium. Stir in the purée, oregano and cinnamon for 2 minutes. Over the next 3 minutes, carefully add the measured water, scrape the base and stir in all the tomatoes, 3g salt and 0.4g pepper, bringing the mixture to a simmer. Simmer uncovered over medium-low heat for about 25 minutes, stirring so the base does not catch. The sauce should cling to the meat, with no puddle of thin tomato liquid; a spoon channel should remain visible briefly. Extend the simmer if it is still watery. Near the end, stir thoroughly and use a clean food probe in the centre and two other thick parts: each must reach 75°C for 30 seconds. These checks are included in the simmer time. Continue cooking and recheck if needed; browning alone does not show that mince is cooked. Clean the probe after use.

As soon as cooking ends, spend about 2 minutes dividing the filling between the shallow heatproof containers, no deeper than about 2cm. Stand them in a basin of cold water, with the water below the rims, and stir the food with a clean spoon to release heat. Allow about 20 minutes for this cooling, replacing the surrounding water when it warms. Prevent any bath water from entering the containers. When the filling is no longer hot or warm, allow about 3 minutes to dry the outsides, cover, label with its cooking time and refrigerate, keeping it separate from raw food. The cooling time is an estimate, not a temperature guarantee: if it is still warm, continue active cooling with fresh cold water or divide more thinly, rather than sealing a warm mass in the fridge. FSA advice is to cool cooked food and put it in the fridge within 1–2 hours; do this as quickly as possible and no later than 2 hours after the filling finished cooking, including portioning and packing. If that has not happened, do not keep it for this recipe. Finish cooling and refrigerating the filling before starting the aubergines; do not leave the pan out for the rest of the session.

Set the oven to 220°C conventional / 200°C fan. Allow 20 minutes for washing, trimming, weighing and slicing the aubergines, lining the trays, and brushing both sides of the slices with oil; the oven preheats during this preparation. Allocate 15ml oil to each 450g group. Lay the slices flat without overlapping. Check actual fit before roasting: if a group is crowded, divide it into smaller loads and share that group's measured oil between them. Extra loads do not receive extra oil. Keep any unroasted slices in the fridge until their turn. Wait for the oven to reach its setting if it takes longer than the preparation.

Roast the first 450g group on the middle shelf for about 25 minutes, turning the slices midway. Look for patches of gold and a soft centre that bends easily; continue roasting if the centre remains firm. Put the tray on the cooling rack and leave the slices spread out for about 20 minutes, protected from raw food and splashes, until no longer hot or warm. Then allow about 3 minutes to transfer them into shallow containers, cover, label and refrigerate. Do not heap hot slices in a deep bowl. If cooling takes longer, keep the slices spread out and refrigerate as soon as cool; the entire roast-end-to-fridge period, including packing, must stay within the FSA two-hour limit. Do not keep a load for this dish if that limit has been missed. This sequence completes cooling and chilling one load before roasting the next, so no tray waits out while sauces are cooked.

Roast the second group in the same oven for about 25 minutes, turning midway, then give it the same approximately 20-minute single-layer cooling and 3-minute packing and refrigeration. Use the same tenderness cue and two-hour roast-end-to-fridge limit for this load separately. If you planned extra smaller loads, repeat the roast, cooling and packing sequence for each one, refrigerating each before starting the next; smaller loads may reach the tenderness cue sooner. Switch off the oven once roasting is finished. Keep all containers covered in the 0–5°C fridge overnight. The timing estimate allows 12 hours from refrigeration of the last load to the start of the next session; this is a scheduling allowance, not a minimum safe chilling time. All components must be thoroughly chilled before the next session. Use the filling and aubergines within 48 hours of cooking, counting from the earliest component, and allow time for baking, resting and serving inside that limit. A different overnight interval changes the total elapsed time by the same amount; do not reset the storage clock when assembling. As a planning allowance, each extra smaller load adds about 25 minutes roasting, 20 minutes cooling and 3 minutes packing: 48 minutes before the overnight interval starts. Use the actual tenderness and cooling endpoints, not that estimate alone.

Keep the cooked containers refrigerated. Heat the oven to 190°C conventional / 170°C fan and allow 20 minutes for preheating while you grate the Parmesan, measure the topping ingredients and remaining seasonings, and set out the dry, room-temperature baking dish and clean layering utensils. Check the dish's working space now if you have not already done so: all the food must fit with 2cm headroom. Choose a larger oven-safe dish now if needed, not after the sauce is made. If the oven is slow, finish waiting for it to reach temperature before starting the topping. Keep the milk and cheese cold until used.

Melt the butter in the saucepan over low to medium heat for about 2 minutes. Whisk in the flour and stir for 2 minutes without letting it colour. Gradually whisk in all the cold milk over about 6 minutes, smoothing each addition before adding more and bringing the sauce towards a gentle simmer. Stir and whisk for another 5 minutes until it is thick enough to spread and a spoon drawn through it leaves a short-lived trail. If it is thin, cook a little longer. Remove from the heat and stir in all the Parmesan and nutmeg, the remaining 1g salt and 0.2g pepper. There is no egg to temper and no sauce-cooling wait: proceed straight to layering.

Allow about 10 minutes for layering. Take all the filling and aubergine containers from the fridge together at the start of this step; do not bring them to room temperature first. Arrange half the roasted aubergine across the base of the ungreased dish, spread all the cold lamb filling over it and cover with the remaining aubergine. Spoon the freshly made topping over the surface and smooth it to the edges. Leave the required 2cm headroom and put the dish into the ready oven straight away. Do not leave the assembled bake waiting for later. If interrupted before this step, leave the components in the fridge and defer making the topping, rather than preparing hot sauce to wait.

Bake on the middle shelf for about 60 minutes at 190°C conventional / 170°C fan. The top should colour to gold, with bubbling around the sides, but these signs do not establish that the cold filling is hot through. Towards the end, check the centre and two other thick areas with a clean food thermometer, including the lamb layer: each checked place must reach 75°C for 30 seconds, and the food should be steaming hot throughout. The checking and holds are included in the baking allowance. Continue baking and check again if necessary; cover loosely with foil if the surface browns before the centre is ready. Clean the probe after use. This is the single reheating of the previously cooked filling and aubergine, not a way to repair missed cooling or poor storage. Lift onto a heatproof surface and rest for 20 minutes, then divide into four and serve promptly. Expect soft, spoonable layers rather than guaranteed straight-sided slices. Cook for the intended meal: do not plan to cool and reheat this bake again, since the filling and aubergine have already been reheated once.