Toss together first 4 ingredients in a medium bowl.
Whisk together flour and next 4 ingredients in a large bowl.
Cut cold butter into flour mixture with a pastry blender or fork until crumbly.
Add buttermilk, stirring just until dry ingredients are moistened. Turn dough out onto a lightly floured surface, and knead 3 to 4 times. Pat into a 6- x 4-inch (1-inch-thick) rectangle.
Cut into 6 squares; cut squares diagonally into 12 triangles.
Arrange 12 (3 1/2-inch) lightly greased miniature cast-iron skillets on an aluminum foil-lined baking sheet. Divide berry mixture among skillets.
Place 1 dough triangle over berry mixture in each skillet.
Bake at 400 for 20 to 24 minutes or until fruit bubbles and crust is golden brown. Cool 15 minutes before serving.