Polenta Biscuits with Sausage Gravy

Name: Polenta Biscuits with Sausage Gravy
Ingredients: Polenta biscuits:; 2 cups all-purpose flour; ½ cup fine or medium-ground cornmeal; 2 teaspoons baking powder; 2 teaspoons sugar; 1 teaspoon salt; ⅛ teaspoon baking soda; ⅔ cup buttermilk; 10 tablespoons unsalted butter, melted; Sausage gravy:; 1 pound breakfast sausage, casings removed; ½ cup all-purpose flour; 5 cups whole milk; ½ teaspoon freshly ground black pepper; ½ teaspoon red pepper flakes; 2 sprigs sage; 1 bay leaf; 1 tablespoon red wine vinegar; ¾ teaspoon salt