01 - Preheat oven to 350°F. Grease and flour a 9-inch round cake pan.
02 - In a medium bowl, whisk together flour, baking powder, cinnamon, nutmeg, and salt until well blended.
03 - In a large bowl, beat butter and sugar until light and fluffy. Add eggs one at a time, mixing well after each addition, then stir in vanilla.
04 - Alternately add flour mixture and milk to butter mixture, beginning and ending with flour. Mix until just combined.
05 - Gently fold sliced apples into the batter. Spread evenly into prepared pan.
06 - Mix 2 tablespoons sugar with ½ teaspoon cinnamon. Sprinkle evenly over the top of the cake batter.
07 - Bake for 50 to 55 minutes until a toothpick inserted in the center comes out clean. Cool in pan for 10 minutes, then transfer to a wire rack.
08 - While cake cools, heat milk in a saucepan until just simmering.
09 - Whisk egg yolks, sugar, and cornstarch in a bowl until smooth and creamy.
10 - Gradually whisk hot milk into yolk mixture. Return mixture to saucepan.
11 - Cook over medium-low heat, stirring constantly, until custard thickens, about 5 minutes. Do not allow to boil. Remove from heat and stir in vanilla.
12 - Serve cake warm or at room temperature with warm vanilla custard poured over each slice.