Instructions

1. 1

   Preheat the oven to 350F and grease a 9 inch springform pan.

2. 2

   Make the custard sauce ahead of time. Bring the milk to a simmer over medium heat. Meanwhile whisk the yolks and sugar until well combined. Drizzle a little of the hot milk into the egg mixture, whisking all the time. Drizzle a little more, then transfer that back into the pan of hot milk and continue cooking, stirring constantly, until the mixture coats the back of a spoon.

3. 3

   Pour the custard through a sieve into a heat proof jar or bowl and place a piece of plastic wrap onto the surface so it won't form a skin as it cools.

4. 4

   To make the streusel topping, blend the bits of butter into the flour, sugar, and oats until the butter is incorporated and the mixture has a coarse crumbly texture. Put in the refrigerator.

5. 5

   Cream together the butter and sugar until light and fluffy. Beat in the eggs, one at a time.

6. 6

   Whisk together the flour, baking powder, cinnamon, and salt. Fold the dry ingredients into the butter/sugar mixture, along with the milk or cream.

7. 7

   Spoon the batter into your prepared pan, and smooth out evenly. Top with the sliced apples, and then the streusel topping.

8. 8

   Bake for about 50 minutes to an hour, until the top is lightly browned and a toothpick comes out without wet batter clinging to it.

9. 9

   Let cool a bit in the pan before removing. Dust with confectioner's sugar before serving.