Mushroom Bourguignon

Name: Mushroom Bourguignon
Ingredients: ¼ cup dried porcini (about 0.3 oz.) or other dried mushrooms; 8 Tbsp. (1 stick) unsalted butter, divided; 2½ lb. mixed mushrooms (such as crimini, button, portobello, and/or baby shiitake), cut into 1 pieces, divided; 3 Tbsp. all-purpose flour; 2 large carrots, peeled, sliced ½ thick on a deep diagonal; 10 garlic cloves, finely chopped; 1 14.4-oz. bag frozen pearl onions; 2 Tbsp. double-concentrated tomato paste; 1½ cups dry red wine (such as Burgundy); 5 sprigs thyme; 1 dried bay leaf; 1 Tbsp. soy sauce; 2½ tsp. Diamond Crystal or 1½ tsp. Morton kosher salt, plus more; Freshly ground pepper; 2 Tbsp. extra-virgin olive oil; 8–12 oz. maitake or oyster mushrooms, torn into bite-size pieces; Mashed potatoes, cooked polenta, or buttered cooked egg noodles (for serving); Sherry vinegar or red wine vinegar (for drizzling)