Combine flour, 1/4 cup sugar, soda, and salt in a large mixing bowl; cut in 1/3 cup butter with a pastry blender until mixture resembles coarse meal.
Combine buttermilk and egg, beating well. Add to flour mixture; stir with a fork until a soft dough forms. Pat half of dough into a well-greased 9-inch round cake pan. (Dough will be sticky; dust hands with flour. )
Spread 1/2 cup butter evenly over dough in pan; pat remaining dough evenly over butter layer. Bake at 425° for 20 minutes or until golden brown. Remove from pan while still warm; split the 2 layers.
Beat whipping cream until foamy; gradually add remaining 1/4 cup sugar, beating until soft peaks form.
Place 1 cake layer on serving plate. Arrange sliced strawberries on top of cake layer. Sprinkle with 1/4 cup powdered sugar. Cover with remaining cake layer, and sprinkle remaining 2 tablespoons powdered sugar over top. Garnish shortcake with whole strawberries. Serve with sweetened whipped cream.