Drain the sweetbreads in cold water for 1 hour.
Drain them, immerse them in a pan of water, bring to the boil for 2 minutes. Cool them under running water. Press them in a tea towel. Remove the firmest membranes. Book.
Peel the shallots, chop finely. Cut off the stumps of the mushrooms. Wash the heads, wipe them.
Peel the potatoes. Leave the BF 15s whole. Cut the rosevals into rings.
Bring a pot of salted water to a boil with a tablespoon of coarse salt, cook the potatoes in it. Let them cook for 25 to 30 minutes.
At the same time, brown the minced shallots with 25 g of butter in a sauté pan over medium heat, stirring often. Add the mousserons and the sweetbreads in small pieces. Salt, pepper.
Continue browning for 2 minutes, moisten with the veal stock and 10 cl of water. Cover and simmer for 20 minutes, stirring occasionally.
At the end of cooking, the juice will be very concentrated and coating.
Preheat the oven to 230°C (th.7/8).
Cook the roseval slices for 5 minutes in salted boiling water. Drain them.
Mash the potatoes with a fork, adding a little cooking water and 100 g of butter.
Spread the sweetbread preparation in an earthenware dish, then the mash on top. Smooth with a spatula. Arrange the roseval slices nicely. Scatter over the remaining shavings of butter.
Bake for 10 minutes in the oven.
Serve with a mesclun.
Small summary of the mousserons:
The only ones who have the right to the name of mushrooms are those of Saint-Georges. Lamellar whites with a delicate aroma of flour and fresh yeast.
Light brown, velvety false mushrooms are marasmus oreads. also nicknamed mountain nymphs, or "Clitopile", "Little Plum", "Tricholome" they grow in a circle in the meadows.
The difficulty:you can find them on markets in the provinces, but they are still very expensive, even better when you are lucky enough to have mousseronières in your garden! which is my case.
