Step by step recipe:

1. 10 min.
   Prepare 2 leeks.
   
   Set aside.
2. 5 min.
   Briefly rinse 400 g mushrooms, dry them, then cut into small pieces.
   
   Set aside.
3. 3 min.
   Prepare 2 shallots and chop finely. Set aside.
4. 5 min.
   Put 2 tablespoons goose fat into a large saucepan on high heat. When good and hot, add the mushrooms.
   
   Sauté for a few minutes until lightly browned. Salt and pepper only after cooking.
   
   Set aside.
5. 1 min.
   Use the same pan, still on high heat. Pour in 4 tablespoons olive oil and when hot, add the shallots.
   
   Salt and pepper, then cook fro 1 minute without colouring.
6. 4 min.
   Add the chopped leeks and mix well.
   
   Cook until the leeks are just tender, but still nice and green (about 3 or 4 minutes).
   
   Preheat the oven to 360°F (180°C).
7. 10 min.
   Add the mushrooms to the pan with the leeks and pour in 250 ml liquid cream.
   
   Turn down the heat and leave uncovered to thicken gently.
   
   Check the seasoning.
8. 1 min.
   Melt 4 tablespoons Clarified butter (this makes it easier to spread).
   
   Using a brush, generously butter the bottom of a round springform tin.
9. 1 min.
   Lay the first buckwheat pancake in the tin, then brush this with butter.
10. 1 min.
    Lay the second pancake on top. You can use clothes pegs at this stage to hold the sides and stop them from falling in.
11. 2 min.
    Fill the tart, then remove the pegs and butter the edge of the pancake that is still showing.
12. 30 min.
    Bake for about 30 minutes.
    
    Serve hot or warm.