In a medium bowl, whisk together the flour, granulated sugar, baking powder, nutmeg, salt and lemon zest.
With a pastry blender, two knives or your fingers, blend in 1/2 cup butter until crumbly.
In a small bowl, whisk together the egg and cream. Add to flour mixture and mix just enough to incorporate; do not overmix.
Press the dough evenly into the bottom of the cake pan. Place the blueberries, raspberries and diced apples on top of the dough and sprinkle with the brown sugar. Place the remaining 2 tablespoons butter pieces over the fruit.
Bake for 20-25 minutes, or until golden brown. Cool on a wire rack. Remove cake from the pan, slice it and serve with whipped cream or vanilla ice cream.