For Crumble

1. In a medium bowl, whisk together the flour, granulated sugar, brown sugar, and cinnamon.
2. Pour the melted butter into the dry ingredients and combine with a spatula. Let the mixture come to room temperature while making the batter.
3. Once the mixture has firmed up, use your hands to break up the mixture into small (about pebble-sized) crumble pieces. Set aside.

 For Cake

1. Adjust oven rack to lower-middle position and preheat oven to 350˚ F.
2. Lightly grease a 10 cup bundt or tube pan. If using a regular 9 x 9 baking pan, line the bottom and sides with parchment paper, allowing the ends to hang over for easy removal of the cake after baking.
3. Whisk together flour, baking powder, baking soda, and salt into a medium bowl. Set aside.
4. Add butter and sugar to the bowl of a standing mixer and mix on medium until light and fluffy, about 2 minutes. Scrape down the sides before adding the eggs, buttermilk, and vanilla extract. Mix until combined. Scrape down the sides.
5. Turn down the mixer speed to low and add the dry ingredients, one third at a time. Mix until just combined. Once combined, remove bowl from standing mixer and give one final turn of the bowl to make sure all ingredients are incorporated.
6. Pour two-thirds of the cake batter into the pan. Carefully spread the batter in an even layer in the pan with an offset spatula. Using clean hands, sprinkle one-half of the crumble filling in an even layer on top of the batter. Then add the final one-third of the cake batter on top of the crumble. It is easier to spoon the remaining one-third of the batter in little piles all over the crumble instead of pouring all of the batter in one mound. Use the offset spatula to carefully cover the crumble layer. Put in the oven for about 25 minutes.
7. After 25 minutes, take out the pan and sprinkle the remaining one-half of crumble mixture on top of the cake. Put back in the oven for 10-15 more minutes, checking often.
8. The cake is done when a toothpick comes out clean and with a few crumbs remaining. Let the cake cool in pan for 15 minutes before carefully removing from the pan. Cool on a wire rack until completely cool before adding glaze.

For Vanilla Glaze

1. While the cake is cooling, whisk together the powdered sugar, vanilla extract and milk. Start with 2 tablespoons of milk because you want the glaze to be very thick.
2. Drizzle the glaze on top of the cooled cake.