Preheat your oven to 375°F (190°C) and grease a 9-inch round cake tin.
In a large mixing bowl, combine flour and baking powder, then rub in the cold diced butter until the mixture resembles breadcrumbs.
Add sugar, cinnamon, and nutmeg to the flour mixture, and mix well.
Stir in the sliced apples, ensuring they are completely coated with the flour mix.
Mix the beaten egg with enough milk to make the wet ingredients up to 150ml. Add to the flour and apple mix and stir to a thick batter.
Pour the batter into the prepared cake tin, spreading it evenly, and sprinkle the top with granulated sugar.
Bake in the preheated oven for 50 minutes or until a skewer inserted in the center comes out clean.
Allow the cake to cool in the tin for about 10 minutes before transferring to a wire rack to cool completely.
Serve warm or at room temperature, ideally with a drizzle of custard or cream.