Picadillo Arepa Pie

Preheat oven to 450°F with rack in middle.

Cook onion and garlic in oil with 1/4 teaspoon each of salt and pepper in a 12-inch heavy skillet over medium-low heat, stirring, until onion is softened, 3 to 5 minutes.

Add beef and cook over medium heat, stirring and breaking up lumps, just until no longer pink. Stir in remaining ingredients with 1/4 teaspoon salt and 1/8 teaspoon pepper and simmer, stirring occasionally, until thickened, 10 to 15 minutes.

Transfer to a 1 1/2- to 2-quart gratin or other shallow baking dish.

Stir together flours, baking powder, baking soda, and salt. Blend in butter using a pastry blender or your fingertips until mixture resembles coarse meal.

Add buttermilk, stirring just until dough is moistened (do not overmix). Dollop over picadillo and bake until topping is golden and cooked through, about 20 minutes.

Let stand 10 minutes before serving.

Picadillo can be made 1 day ahead and chilled. Reheat before adding topping.