Cornbread with soda

4 tablespoons unsalted butter 3 cups cornmeal 2 teaspoons cream of tartar 2 teaspoons salt 1 teaspoon baking soda 3 cups low-fat milk 4 large eggs 9 ounces[...]

8 tablespoons chilled unsalted butter , cut into 1/2 inch pieces 1 cup chopped onion 1 3/4 cups yellow cornmeal 1 1/4 cups all-purpose flour 1/4 cup sugar 1[...]