STEP 1
Peel the potatoes, slice them and put them in a saucepan along with the chopped leeks. Put half under water and cook for 15 minutes until the vegetables are soft. Drain the water and put the saucepan on the stove for a while longer, allowing the remaining water to simmer out. Add in the butter and a pinch of pepper, salt and nutmeg and mash with a masher.
STEP 2
Make the cheese sauce. Mix the milk with the vegetable stock in a saucepan and bring the mixture to a boil over medium heat. When the milk is well warm, add the roux to it while continuously stirring with a whisk, so that the milk does not stick to the bottom and create lumps. After a minute on the heat, add 70 grams of grated cheese. Stir well and season if necessary.
STEP 3
Preheat the convection oven to 180°C. Mix the minced meat with the chopped onion and season with a pinch of salt and pepper. Put 1 tablespoon of fat in a pan and briefly fry the seasoned minced meat.
STEP 4
Take a baking dish and put the puree in the dish as the first layer. Then divide the minced meat over the puree. Put the cheese sauce on top as the last layer and sprinkle the remaining 30 grams of grated cheese over the cheese sauce. Bake the casserole for 25 minutes in the oven at 180 °C, putting it on grill mode for the last 5 minutes for a crispy crust.