Preheat Oven: Set oven to 400°F and place rack on lowest level.
Mix Dry Ingredients: Whisk flours, sugar, baking soda, cream of tartar, and salt in a bowl.
Add Butter: Work in softened butter until mixture resembles coarse crumbs.
Add Buttermilk: Stir in buttermilk until no dry streaks remain. Add 1–2 tablespoons more if needed.
Shape Dough: Lightly flour surface and form dough into a rough 6-inch mound.
Score Top: Use serrated knife to cut a deep cross on top.
Bake: Bake for 35–40 minutes until deep golden brown and a toothpick comes out clean.
Brush & Cool: Brush with melted butter and let cool 30–45 minutes before slicing.
