1. Reserve 6 strawberries. Slice remaining berries; in bowl, gently stir together sliced berries and 1/4 cup granulated sugar. Heat oven to 450°F. Grease 8-inch round baking pan.
2. Stir together flour, cocoa, remaining 1/2 cup granulated sugar, baking powder and salt in medium bowl; cut in butter until mixture resembles coarse crumbs. Stir together milk and egg; add all at once to dry ingredients, stirring just until moistened. Spread dough in prepared pan, building up edges slightly.
3. Bake 15 to 18 minutes or until wooden pick inserted in center comes out clean; cool 10 minutes. Remove from pan; place on serving plate. Beat whipping cream and powdered sugar until stiff. Arrange some sliced berries over cake; top with whipped cream. Garnish with reserved whole strawberries; serve with remaining sliced berries. Makes 12 servings.