Clean the broccoli and cauliflower, quarter them and cut into pieces. Bring 700 ml broth to the boil, blanch broccoli and cauliflower in it for about 5 minutes. Pour broccoli and cauliflower into a sieve and drain.
Peel onions and cut them into fine pieces. Grate cheese. Melt the fat in a pot. Stir in flour, sweat briefly. Add milk and 250 ml broth bit by bit while stirring. Bring to the boil, simmer for 6-8 minutes, remove from heat.
Add 50 g of cheese to the sauce and let it melt. Season to taste with salt, pepper, nutmeg and lemon juice.
Arrange the vegetables in a greased, ovenproof casserole dish (22 cm Ø; 4.5 cm high). Pour Bechamél sauce over it and sprinkle with remaining cheese. In a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see
manufacturer) bake for 20-25 minutes.
In the meantime cut the bread into small cubes. Wash the thyme, shake dry and remove the leaves. Chop the almonds coarsely. Mix bread cubes, thyme and almonds. Switch the oven to grill level.
Carefully remove the casserole dish from the oven. Sprinkle bread cube mixture over it and roast it under the hot grill for another 4-5 minutes. Remove, sprinkle with some coarse sea salt and serve immediately.