Preheat oven to 350 degrees F (175 degrees C).
In a large bowl, mix flour, 1/4 cup sugar, baking powder and cream of tartar. Cut in butter with pastry blender or two knives. Stir in cream and egg. Turn out onto a lightly floured surface and knead 2 minutes. Press into a half-inch thick sheet. Cut into squares. Place on baking sheets.
Bake in preheated oven 20 minutes, or until golden. Sprinkle 3 tablespoons sugar over sliced berries.
Let shortcakes cool before splitting and filling with sugared berries.