1. To make the topping, mix the flour, sugar, and cinnamon in a bowl. Add the butter and rub it in. Shape into a thick disk, wrap in plastic wrap, and refrigerate for 30 minutes.

2. Preheat the oven to 375°F (190°C). Butter an 8-in (20cm) springform pan and line the bottom with wax paper. Peel and core the apples, and cut them into wedges.

3. Beat the butter, sugar, and lemon zest together until pale and creamy. Beat the eggs, one at a time, into the butter mixture. Sift the flour, baking powder, and salt together. Add to the bowl, along with the milk, and mix until smooth.

4. Spread half of the batter into the pan. Top with half of the apples. Repeat. Grate the streusel over the apples.

5. Bake for 45–50 minutes, or until a toothpick inserted into the center comes out clean. Let stand on a wire rack for 10 minutes. Remove the sides of the pan and cool. Serve warm or cold.