To prepare topping, stir together flour, brown sugar, baking powder and salt in a large bowl. Add butter and cut into flour mixture using a pastry blender or 2 forks until mixture resembles coarse crumbs. Stir in milk and vanilla until a soft dough forms. Divide dough into 12 pieces and place onto peach mixture. Brush tops of dough pieces with milk and sprinkle with sparkling sugar.