Apfelkuchen mit Streuseln (apple streusel cake)

Method

1. Rub the cold butter into the flour, sugar, baking powder and salt until it looks like coarse crumbs, then work in the egg just until a dough forms. Press into the base of a 26 cm springform, about 2 cm up the sides, and chill for 20 minutes.
2. Make the streusel: rub the cold butter into the flour, sugar and vanilla sugar with your fingertips until it forms coarse, pea-sized crumbs. Chill until needed.
3. Toss the apple slices with the lemon juice, sugar and cinnamon.
4. Arrange the apples evenly over the chilled base, then scatter the streusel over the top in an even, generous layer.
5. Bake at 180°C for 40 to 45 minutes, until the streusel is solidly golden brown and a skewer meets no resistance in the apples underneath.
6. Cool in the tin for 20 minutes, then release the sides and cool completely on a rack before slicing.

Notes

• Keep the streusel cold until it goes into the oven. Warm butter in a streusel mixture melts into a solid sheet instead of baking into distinct crumbs.
• A mix of tart and sweet apple varieties gives more depth than a single variety; Elstar with a handful of Boskoop is a good German combination.
• Do not slice the apples too thin. Very thin slices collapse under the streusel and the middle of the cake loses definition; aim for slices about half a centimetre thick.
• It keeps for 3 days at room temperature under a cake dome, or 5 days in the fridge, though the streusel softens somewhat once refrigerated.

Ingredient substitutions

• Apples can be pears in the same weight, with the cinnamon reduced slightly since pears carry a more delicate flavour.
• Vanilla sugar in the streusel is a small, traditional touch; plain sugar works identically if it is not to hand.
• For a nuttier streusel, replace 30 g of the flour with 30 g of finely chopped almonds or hazelnuts.
• A layer of marzipan crumbled over the apples before the streusel goes on is a common and welcome regional variation.