Bring 5 cups of water to a boil add the salt and the polenta, then reduce for a simmer - allow to cook for 30 mins-40 mins
Stir in the butter
For the Mushroom Bourgignon:
Heat the butter and oil over medium heat in a large bottomed pan. Add the chopped mushrooms and brown.
When the mushrooms have browned, remove them from the pan.
Add another tablespoon of butter, then add the carrots and onion to the pan along with the rosemary and thyme. Season with salt and pepper.
Saute the veggies for 5-7 minutes or until the carrots and onions begin to brown.
Add the wine and crushed garlic to the pan and use a wooden spoon to deglaze the bottom of the pan.
Stir in the tomato paste and add the stock. Increase the heat to high and bring the pot to a boil, then reduce the heat to a simmer. Simmer for 10 minutes, then add the mushrooms back to the pot. Continue to simmer until the liquid has reduced by about half. Remove a couple of tablespoons of sauce from the pan and stir in the corn starch.
Add the slurry to the pan, increase the heat to high, and stir until the sauce thickens.