Place 4 Tbsp. butter in a 10-inch cast-iron skillet, and put skillet in a 350° oven 10 minutes or until butter is melted.
Meanwhile, toss raspberries with 3/4 cup sugar in a large bowl.
Sift together 1 1/2 cups flour, baking powder, and salt in a medium bowl. Stir in milk, vanilla, and remaining 1/4 cup sugar.
Add hot melted butter to flour mixture, and stir until blended. Pour batter evenly into skillet. Pour berry mixture into center of batter.
Bake at 350° for 50 minutes or until top is golden brown and a wooden pick inserted in crust comes out clean. Let stand 10 minutes. Serve with vanilla ice cream, if desired. Garnish, if desired.
*2 (12-oz.) packages frozen mixed berries may be substituted for frozen raspberries.