Make the glaze: In a small bowl, whisk together all the ingredients until smooth and set aside.

Make the crumble: In a small bowl, whisk together the sugars, flour, and salt. Drizzle the melted butter over the top, and using a fork, mix until clumps form. Do not overmix! Only mix until clumps form and no further. Place the bowl in the fridge until ready to use.

Prepare the apples: In a bowl, toss the chopped apples with the remaining ingredients and set them aside.

Make the cake: Preheat an oven to 350 degrees F. Lightly grease an 8x8 baking dish and line the bottom with parchment paper. In a small bowl, whisk together the flour, baking powder, baking soda, and salt and set aside.

In a larger mixing bowl, use a hand mixer to beat the butter until fluffy, about 1 minute. Add both sugars and beat for another 2-3 minutes until the sugar and butter is light and fluffy. Scrape down the sides of the bowl if needed. Add the room temperature eggs and beat until smooth and well-mixed; if the mixture looks a little curdled, that's okay!

Next, add the sour cream and vanilla and beat until smooth. Add the flour mixture and mix for 15-20 seconds, until JUST combined (don't over mix!). If there are still clumps of flour, use a rubber spatula to gently fold the mixture together.

Spread the batter in an even layer in the prepared pan using an offset or rubber spatula. Top with the apples and any juices that have accumulated in the bowl. Remove the crumble from the fridge and toss with a fork, then top the apples with the crumble.

Bake for 45-50 minutes or until a cake tester inserted in the middle of the cake comes away clean. Allow to cool for 20 minutes and then remove the cake from the pan. Cut into pieces and drizzle with the maple-vanilla glaze.