Preheat the oven to 350°F (180°C/Gas Mark 4). Butter a 10-inch pie pan.
Mix the flour with the baking powder. Rub in the butter with your fingertips until the texture resembles bread crumbs. Add the ½ cup sugar, beaten egg, and enough milk to form a soft dough. Pat out half of the dough in the greased pie pan (it is supposed to be very wet).
Peel, core, and chop the apple into ¾-inch (2cm) cubes. Arrange the apples on the dough and sprinkle with 1 tablespoon sugar and the cinnamon.
Gently spoon out the remaining dough on top of the apples to cover them completely. Sprinkle with the remaining 1 tablespoon sugar and cut a slit through the middle of the top dough.
Bake for 40 to 50 minutes, until golden and crunchy on the outside (the apples should be soft on the inside).