Crumble

1. Cut your cold butter into small cubes 
2. In a small bowl, combine flour, brown sugar, steel-cut oats, and cinnamon
3. Add the cold cubed butter to the dry ingredients. Using your fingers or a pastry cutter work together the butter and dry ingredients until it starts to clump together
4. Place your crumb mixture in the refrigerator while you prepare the donut batter

Donut

1. Preheat oven to 350 degrees. Grease your donut pans and set them aside 
2. In a medium bowl, whisk together flour, brown sugar, baking powder, cinnamon, and salt
3. In another bowl, whisk together eggs, sour cream, melted butter, and vanilla until combined 
4. Fold the wet ingredients into the dry ingredients until just combined
5. Pipe the batter into donut pans using a pastry bag or ziplock bag
6. Evenly and generously top each of the donuts with the already prepared crumble
7. Bake for 10 - 12 minutes, using a toothpick to check for doneness 
8. Once done, let them rest in the pan and cool for 10 minutes
9. Remove from pan and place on a cooling rack

Vanilla Glaze

1. While your donuts are in the oven prepare the glaze
2. Whisk together powdered sugar, milk, and vanilla until fully combined and there are no clumps
3. Once your donuts are on the cooling rack you can drizzle the glaze over each of the donuts**