Cook bacon in the oven until crispy, on an aluminum foil covered baking sheet, at 400 degrees. Time of cooking will depend on the thickness of the bacon you are using. Save the grease from baking the bacon. Crumble and dice cooked bacon and set aside.
Doughnuts:
Preheat the oven to 350 and grease a doughnut pan.
In a large mixing bowl, whisk egg, sugar, milk, sour cream, bacon grease, and vanilla together until smooth.
Sift in all dry ingredients (not bacon crumbs) and whisk until all incorporated.
Sprinkle some bacon crumbs at the bottom of each doughnut cup of the baking pan.
Pour the batter into a piping bag. (You may have to pour some batter in and refill later.)
Cut the tip off the piping bag, leaving only about ½ inch opening.
Squeeze batter into the doughnut cups of the pan, in a circular motion. Make sure there is an even amount of batter all around. (Refill the piping bag when needed.)
Sprinkle crumble topping on top generously.
Bake for 15-18 minutes and let doughnuts cool on the wire rack.
Crumb topping:
In a medium bowl, combine brown sugar, white sugar, and flour. Mix well until all ingredients are incorporated evenly.
Pour in bacon grease and melted butter and carefully fold it in with a large fork. You will want to be careful so you don’t over-mix. Crumb topping should look like large crumbs and not paste.
Glaze:
Warm up heavy cream but not too hot. Add powder sugar to a shallow bowl and whisk in heavy cream slowly, until all smooth. Place in a piping bag. Cut of a tiny tip at the end of the piping bag. Drizzle warm doughnuts, not hot doughnuts or icing will melt.