Finns use a lot of mushrooms and many enjoy mushroom picking, so delicious mushroom pies are very popular vegetarian option. This crust works well for other pies as well, and there is no need to pre-bake the crust!
The Finnish forests have a lot of variety in mushrooms and many are excellent food. My favorite ones are normal yellow chantarelles and darker funnel chanterelles (wikipedia link), which can be picked until the snow arrives. Mushroom picking is great fun, once you find a few, you can find hundreds!
For this recipe you can use naturally also fresh mushrooms.