Preheat oven to 375°

Topping

1. Combine the two sugars, flour, and cinnamon in a spacious mixing bowl.

2. Add the melted butter and zest and use your fingers to toss and pinch the ingredients together, forming a coarse, crumbly mixture. Set aside.

Muffin

1. Place the sugar in a spacious mixing bowl.

2. Sift in the flour, baking powder, baking soda, and salt. Whisk to combine.

3. In a separate bowl, whisk together the eggs, buttermilk, orange zest, vanilla and melted butter.

4. Stir the egg mixture in to the dry ingredients and mix until combined but still lumpy—Do not beat smooth.

5. Fold in the blueberries and mix until evenly distributed.

6. Divide the batter evenly among the prepared muffin cups. The cups will be quite full.

7. Sprinkle the muffins with crumb topping.

8. Bake for 25–30 minutes, or until a toothpick inserted into the center of the muffin comes out clean.