Braised Celery and Sausage

Name: Braised Celery and Sausage
Ingredients: 1 cup chopped onion; 2 finely chopped garlic cloves; 2 tablespoons olive oil; 1 teaspoon kosher salt; ¼ teaspoon black pepper; 1½ pounds sweet Italian sausage; 1 cup white wine; 8 celery stalks, cut into 2-inch pieces; 1 15-ounce can diced tomatoes; Soft polenta and chopped parsley, for serving