Preheat the oven to 350F. Then grease a 9x13 baking dish with a piece of butter.
Place softened butter and white and brown sugar in a large bowl. Combine with a spatula first, then use an electric mixer to cream your mixture until light and fluffy (about 3 minutes). Note: it’s essential that ingredients are at room temperature so butter and sugar emulsion don’t break when adding the eggs.
Add one egg at a time and use a whisk to mix after each addition. Next, add vanilla extract and mix.
In a different bowl, mix flour, baking powder, and salt.
Add ⅓ of the flour mixture into the egg mixture bowl. Stir to combine and add ¼ cup of milk and combine. Follow with ⅓ of flour, stir, and then another ¼ cup of milk. Finish by combining the remaining flour. Set the batter aside.
crumble
Prepare the apple crumble by mixing all the crumble ingredients until well combined.
Pour half of the cake batter into the prepared baking pan, followed by ½ of the apple crumble. Then, add the remaining batter and the crumble on top.
Bake the cake for 50 to 55 minutes or until an inserted toothpick, comes out clean.
Let it cool to room temperature before unmolding it. For the size of the cake, it’s easier to slice it first and then transfer it one piece at a time.
glaze
Combine ingredients in a bowl and whisk. Pour over cake when ready to serve.
Notes
To bring butter, eggs, and milk to room temperature, you can leave them over the counter for one to two hours, depending on the room's temperature.
glaze may be prepared ahead of time and stored in the fridge when ready to serve