1. Preheat oven to 400°. Toss together first 4 ingredients in a medium bowl.
2. 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.
3. 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.
4. Bake at 400° for 20 to 24 minutes or until fruit bubbles and crust is golden brown. Cool 15 minutes before serving. Serve warm or at room temperature.