Clean, wash and cut the leek into rings. Bring the stock to the boil and pre-cook the leek for about 5 minutes and drain. Collect the broth. Measure out 1/2 litre. Drain the pumpkin on a sieve as well.
Stone the olives and chop them coarsely, except for 3 pieces for garnishing. Dice sheep's cheese. Peel garlic and press it through a garlic press. Heat the fat and garlic in a pot and sauté the flour in it.
Add stock and milk while stirring and add thyme. Let the sauce simmer for about 5 minutes and remove from the heat. Mix the egg yolks with some hot sauce and stir into the rest of the sauce. Season to taste with salt and pepper.
Pour a thin layer of sauce into a greased casserole dish and place 4 lasagne plates on top. Spread leek and olives on top and cover with 4 lasagne plates. Pour half of the sauce over it.
Sprinkle pumpkin and feta cheese, up to 50 g, on the sauce and cover with the remaining lasagne sheets. Pour the rest of the sauce over it. Sprinkle with pumpkin seeds and remaining feta cheese. Garnish with the remaining olives.
Bake in the preheated oven (electric: 200°C / gas: level 3) for 45-60 minutes. Serve sprinkled with fresh thyme as desired.