Mix eggs with sour cream in a mixing bowl and start adding the dry ingredients spoon by spoon. Your batter will get thick.
Grease a 15'x11' (40x25 cm) baking pan with some butter and transfer the batter. Spread it nicely to cover the bottom of the pan. Bake it in the oven for 15 minutes at 150ºC (302ºC)
Meat sauce
While the base is baking, melt the butter with olive oil in a deep saucepan. Add the onion and garlic and sauté for 3-4 minutes. Add the minced meat and let it brown. Keep mixing.
Add the chopped tomato and pepper and stir. Start adding bone broth or water little by little. Let the sauce thicken. Add bay leaves.
Add salt, cinnamon, spearmint, oregano and let it simmer for 10 minutes so that the sauce thickens.
When the sauce is thick and creamy, remove it from heat. Add freshly ground pepper and let it cool down a bit. Now add 1 egg and stir well. Remove bay leaves.
Assembling the Pastitsio
Take the base out of the oven and spread the meat sauce on it.
Beat the eggs with sour cream, salt and nutmeg and pour this mixture over the meat sauce.
Bake the Pastitsio in the oven for 25 minutes at 170ºC (338ºF). In the end, sprinkle sheep cheese all over the top and return it in the oven for 5 minutes so that the cheese melts and creates a crisp crust.