Put the corn grits in a saucepan with 2 tablespoons of butter and stock and bring to the boil while stirring. Then reduce the heat and let the polenta swell for about 15 minutes while stirring occasionally.
In the meantime, peel and dice the onion. Clean the mushrooms and cut them into slices. Finely chop the parsley.
Melt the remaining butter. Cook the onions and mushrooms al dente, season with salt and pepper. Stir in the parsley.
Mix the mushroom and onion mixture with the polenta.
Spread the mushroom polenta on a greased tray, allow to cool. Then cut into pieces and fry in the oil on both sides until crispy.