Over a floured work surface, lower puff pastry into a rectangle of 25 cm x 12,5 cm (10 inches x 5 inches). Brush pastry with egg yolk. Slice rectangle into two squares, and each squares into diagonal to obtain four triangles.
Lay triangles over a baking sheet covered with parchment paper. Oven bake for 15 to 20 minutes, until pastry browns.
Meanwhile, melt butter at medium heat in a casserole. Cook oyster mushrooms with leek and garlic for 2 minutes.
Add snails and white wine. Bring to a boil and cook 1 to 2 minutes, until liquid reduce of three quarters.
Add broth, cream and brie. Simmer at medium-low heat for 4 to 5 minutes.
Add tarragon and seasoning.
When serving, slice pastries in two over thickness. Divide snails mixture over half of pastries. Cover with pastries remaining.
Did you know that...
Leeks are full of antioxidants and great for fighting cholesterol and cancer.