Preheat oven to 400°.
Combine first 4 ingredients in a medium bowl. Lightly spoon flours into dry measuring cups; level with a knife. Combine flours, sugar, salt, baking powder, and baking soda in a large bowl; make a well in center of mixture.
Add buttermilk mixture to flour mixture, stirring just until moist; stir in raisins. Stir with a wooden spoon until dough pulls together in a shaggy mass. Let rest 2 minutes.
Turn half of dough out onto a lightly floured surface. Knead 1 minute with floured hands (dough will feel tacky); shape dough into a 6-inch round loaf. Place on a baking sheet dusted with cornmeal. Repeat procedure with remaining dough. Make 3 diagonal cuts 1/4-inch deep across top of each loaf using a sharp knife.
Bake at 400° for 20 minutes. Reduce oven temperature to 375° (do not remove loaves from oven); bake an additional 15 minutes or until bottom of each loaf sounds hollow when tapped. Let stand 15 minutes before slicing.