Preheat the oven to 400°F and grease a 9 x 5-inch loaf pan with solid shortening or nonstick spray.
In a medium bowl, whisk together the flour, cornmeal, baking soda, cream of tartar, salt, and sugar.
In a large bowl, lightly whisk the egg, then add sour cream, milk, and melted butter and mix until smooth.
Add the dry ingredients to the wet mixture and stir just until fully combined. The batter will be thick.
Transfer the batter to the prepared pan and gently level the top.
Bake on the middle rack for 30 to 35 minutes until golden and a toothpick inserted in the center comes out clean.
Cool in the pan for 5 minutes, then loosen and transfer to a wire rack.
Slice with a serrated knife and serve warm.
