Step 1

Crumb topping: Place the melted butter, flour and sugar in a bowl and use a fork to mix until it becomes a coarse crumble. Set aside.

Step 2

Preheat the oven to 350°F (176°C). Line a 12 count muffin tin with paper liners or grease generously to prevent sticking.

Step 3

Dry ingredients: In a large mixing bowl combine the flour, sugar, baking soda, baking powder, corn starch, lemon zest and salt with a fork. Add the blueberries and toss the mixture to coat. Set aside.

Step 4

Wet ingredients: In a medium mixing bowl, whisk all the wet ingredients until smooth. Pour the wet ingredients into the dry ingredients and stir until just combined. (If the batter is too stiff, add 1-2 tablespoons of water or milk to help thin it down.)

Step 5

Divide the batter evenly into 12 muffins and sprinkle the top with the crumble topping. Make sure to press the crumble, gently, on the top of the batter.

Step 6

Bake for 30-35 minutes or until a toothpick inserted into the center of a muffin comes out clean. Let muffins cool in the tin for 10 minutes before removing to cool on a cooling rack.