Beef and Mushroom Stroganoff over Creamy Polenta

Name: Beef and Mushroom Stroganoff over Creamy Polenta
Ingredients: Kosher salt; 1 cup instant polenta; 4 tablespoons olive oil; 2 Spanish onions, thinly sliced; 1 large shallot, thinly sliced; 2 to 3 thyme sprigs; 1 tablespoon minced garlic; Kosher salt and freshly ground black pepper; 4 cups wild mushroom mix; 12 ounces beef sirloin, thinly sliced; 1/4 cup brandy; 1 cup beef stock; 2 handfuls baby spinach, stems trimmed; Sour cream, for garnish; Chopped fresh parsley, for garnish; Lemon zest, for garnish