Bring water to boil. Add salt,reduce heat to medium heat gradually add polenta,whisking constantly. Whisk 5 minutes. Reduce to low,stir occasionally 10 minutes . Add 1/2 c cheese,1 t. thyme and 1/2 t pepper. Stir throughly. Pour into a a baking sheet,cover with wax paper cover with another baking sheet on top. Chill overnight. Cut into bite size shapes. Bake 375 degrees 10-12 minutes. Broil 18 inches 3 minutes until crispy and brown. Top with mushrooms.
Mushroom Topping: heat olive oil and butter,add onions,garlic and mushrooms until mushrooms are tender,season with salt and pepper.