Chili Cheddar Shortcakes

1 1/2 cups all-purpose flour
2 teaspoons double-acting baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
2 tablespoons cold unsalted butter, cut into bits
1/4 pound sharp Cheddar, grated coarse (about 1 1/2 cups)
2 jalapeño chilies, seeded and minced
1 cup sour cream

Into a bowl sift together the flour, the baking powder, the baking soda, and the salt, add the butter, and blend the mixture until it resembles coarse meal. Stir in the Cheddar and the chilies, add the sour cream, and stir the mixture until it just forms a soft but not sticky dough. Knead the dough gently 6 times on a lightly floured surface, roll or pat it out 1/2 inch thick, and with a 3 1/2-inch cookie cutter cut out 6 rounds. Bake the rounds on an ungreased baking sheet in the middle of a preheated 425°F. oven for 15 to 17 minutes, or until they are golden.