For the gnocchi:
Mix the mashed potatoes, the mushroom purée, then add the egg, salt and complete by adding the flour. The consistency should be solid and compact. Make a long cylinder shape from the dough, not too thick, then cut the dough into bite size pieces. Lightly flour if needed and keep them refrigerated at 4° C on a floured cloth until ready to cook.
For the sauce:
Wash and clean the porcini, cut them into 4 pieces and then boil them in lightly salted water that has been flavored with white wine, a few grains of pepper and a bay leaf. Drain and refrigerate at 4°C.
Cook the gnocchi in abundant boiling water, lightly salted. Leave them boil until they float back to the top, around 2 minutes. In the meantime, sautee the porcini, adding a few drops of water, add the goat butter and the freshly chopped thyme. Toss in the gnocchi and serve them when they are well glazed. Place them on the plate and garnish with a sprig of thyme.