Set oven to 350F. Butter a 9-inch round cake pan. Sift together the dry ingredients. Using a food processor with the steel blade or a pastry cutter, cut the butter into the flour mixture until it resembles small peas. Blend in the raisins and caraway seeds. Beat the egg, buttermilk, and sour cream together until blended. Stir the egg mixture into the dry mixture just until blended. Transfer the batter to the pan and bake for about 50 to 55 minutes, until a toothpick inserted in the center comes out clean. Makes 1 loaf.