In a medium pot, saute chopped onion until transparent. Press the garlic into the pot and saute until fragrant.
Add the stock and bring in to boil on medium heat. Add polenta and salt while stirring. Reduce the heat to low and simmer, stirring occasionally until very thick (20-25 minutes.) (Be careful because you can get really burned if it spatters)
Lightly grease a medium casserole dish with 1 tsp of olive oil and transfer the polenta into it. Spread it evenly and let it sit for about 10 minutes. It will mold nicely so you can cut it into squares.
In a medium saute pan, saute onions and mushrooms until almost done. Add salt, pepper and wine. Stir well and cook for a couple of minutes. Add heavy cream and cook for about 5 more minutes.
Stack the polenta squares on a plate and top if off with mushrooms and sauce.
Add some chopped green onion and fresh grated Parmesan cheese on top.