Preheat oven to 350°.
Coat 4 (8-ounce) custard cups or ramekins with cooking spray. Place 1 butter piece in bottom of each cup. Sprinkle 1 teaspoon brown sugar over butter in each cup. Arrange 1 apricot half, cut side up, over brown sugar in each ramekin. Arrange 8 cherry halves, cut sides up, around outside edge of each apricot; set aside.
Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, baking soda, and salt, stirring with a whisk. Place granulated sugar and 2 tablespoons butter in a medium bowl; beat with a mixer at medium speed until well blended. Add vanilla and egg; beat well. Add flour mixture to sugar mixture alternately with milk, beginning and ending with flour mixture; beat well after each addition. Divide batter evenly over fruit in each cup. Place cups on a baking sheet.
Bake at 350° for 30 minutes or until a wooden pick inserted in center comes out clean. Cool in cups 5 minutes on a wire rack. Loosen edges of cakes with a knife. Place a dessert plate, upside down, on top of each cup; invert onto plates. Drizzle any remaining caramelized syrup evenly over cakes. Serve cake warm with whipped topping.