Once the polenta is on the stove, prepare the ragú. Heat the 2 tablespoons olive oil in a large 12-inch nonstick skillet over medium heat. Add the onion and cook for 5-6 minutes, or until lightly browned.
Add the mushrooms and fresh thyme leaves, and cook, stirring occasionally, until the mushrooms are golden, about 5-6 minutes.
Add the cherry tomatoes, black pepper, and 1 1/4 teaspoons kosher salt. Cook until the tomatoes burst, about 6-7 minutes. If the tomatoes or mushrooms start to burn, lower the heat. Pour in the marinara sauce and stir to coat the vegetables.
Pour in the white wine and bring the mixture to a simmer. Cook until the wine is mostly reduced, about 5 to 6 minutes. If desired, turn in the vegan butter and stir in until melted.