01 - Preheat oven to 350°F. Grease and line an 8-inch round cake pan with parchment paper.
02 - In a large bowl, whisk together flour, baking powder, salt, cinnamon, and nutmeg.
03 - Rub in the cold butter with your fingertips until the mixture resembles coarse crumbs.
04 - Stir in ¾ cup granulated sugar until evenly distributed.
05 - In a separate bowl, whisk together eggs, milk, and vanilla extract.
06 - Add the wet ingredients to the dry and mix until just combined.
07 - Gently fold in the diced apples until evenly incorporated.
08 - Pour the batter into the prepared pan, smooth the top, and sprinkle with 2 tablespoons sugar.
09 - Bake for 45–50 minutes, or until golden and a skewer inserted into the center comes out clean. Cool in the pan for 10 minutes, then transfer to a wire rack.
10 - In a saucepan, heat 2 cups milk until just below boiling.
11 - In a bowl, whisk egg yolks, sugar, and cornstarch until smooth and pale.
12 - Gradually pour the hot milk into the yolk mixture, whisking constantly to prevent curdling.
13 - Return the mixture to the saucepan and cook over low heat, stirring constantly, until thickened enough to coat the back of a spoon. Do not let it boil.
14 - Remove from heat and stir in vanilla extract.
15 - Serve warm apple cake slices with generous spoonfuls of warm custard.