Combine the flours, brown sugar, baking powder, cinnamon, baking soda, nutmeg, and salt in a bowl.
Add in the cold unsalted butter that has been cut into pieces. With a pastry blender, cut the butter into the flour mixture until it is crumbly. Set it aside a moment.
Core and dice the apple.
Stir the diced apple into the flour mixture.
Stir in the 2/3 cup of milk, until just combined. Turn the dough out onto a lightly floured surface and knead gently 6-7 times.
Divide the dough in half and form into two 6-inch disks. Cut the disks each into 6 wedges.
Place the wedges on a lightly greased or nonstick baking sheet. Brush the tops with the remaining milk.
Sprinkle with 1/4 teaspoon each of demerara sugar. Bake for 12-15 minutes or until golden. Serve warm.