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1
Preheat oven to 350u00b0F.
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2
Make the custard sauce ahead of time. Bring the milk to a simmer over medium heat. Meanwhile whisk the yolks and sugar until pale. 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. Don't overcook or it can curdle. Stir in the vanilla. Refrigerate the custard sauce until needed.
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3
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.
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4
To make the cake, grease a 9 inch round spring form pan.
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5
Cream together the butter and sugar until light and fluffy. Beat in the eggs, one at a time.
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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.
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7
Spoon the batter in to the pan, and smooth out evenly. Top with the sliced apples, and then the streusel topping.
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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.
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9
Let cool a bit in the pan before removing. Dust with confectioner's sugar before serving.
