1. Preheat the oven to 425 degrees and line a muffin tin with muffin liners.
2. In a stand mixer, cream together the butter and sugar for 1 minute. Scrape down the sides of the bowl. Add the unsweetened apple sauce and egg. Turn the mixer on low and break apart the egg yolk.
3. In a separate bowl mix together all the dry ingredients. With the mixer on low begin to add in the dry ingredients into the wet ingredients. Keep mixing a batter if formed.
4. Scoop the batter into the lined muffin tins. Fill about 2/3rds full.
5. To make the crumb topping, melt the butter. Add the remaining ingredients to the melted butter and mix together until a paste is formed. Spoon even amounts on top of the muffin.
6. Place the muffins in the oven and lower the heat to 350 degrees. Bake for 16-18 minutes.