Pour 2–3 tablespoons of rum over the raisins and let them soak for at least 30 minutes, or longer if possible.

Mix flour, sugar, and salt. Add the cold butter and rub it in with your fingers until crumbly. Add the egg and quickly knead into a crumbly dough.

Use about two-thirds of the dough for the base and sides. Press it directly into a greased and parchment-lined 9-inch (23 cm) springform pan, pressing it evenly over the bottom.

For the sides, roll small portions of dough into logs, place them around the inside edge of the pan, and press up to form a rim about 1–1.5 inches (3–4 cm) high.

Chill the remaining dough (this will become the streusel).

In a saucepan, whisk together cornstarch, sugar, salt, and a small splash of the milk until smooth. Gradually whisk in the rest of the milk, then stir in the ground poppy seeds.

Cook over medium heat, stirring constantly, until the mixture thickens and comes to a gentle bubble. Let it simmer for about 1 minute to fully activate the cornstarch.

Remove from heat. Stir in the rum and vanilla extract.

Drain the raisins and fold the rum raisins into the hot poppy seed custard. Let cool for about 10 minutes.

Peel, core, and slice the apples. Toss them with lemon juice.

Spread the poppy seed custard filling into the prepared crust and smooth the top. Arrange the apple slices evenly over the filling.

Take the remaining chilled dough and mix in the sliced almonds. Crumble it loosely over the apples as streusel.

Bake in a preheated oven at 325°F (160°C) top/bottom heat for about 60 minutes.

Baking at this lower temperature helps the cake bake evenly: the crust doesn’t get too dark, the filling sets gently, and the streusel turns golden without burning.

Alternatively, bake at 350°F (180°C) for 45–50 minutes. If the streusel browns too quickly, loosely cover the cake with foil toward the end of baking.

Let the cake cool completely in the pan before slicing so the filling can fully set.