Preheat oven to 400°F (200°C). For crisper edges, grease a standard muffin pan. For softer edges, use liners in each cup instead.
Using a fork, mix all the crumb ingredients together until well-combined. Set aside.
To make the muffins:
Whisk together the flour, baking powder, baking soda, and salt in a medium-sized bowl. Set aside.
In a large bowl, lightly beat the eggs. Stir in the buttermilk. Add both sugars and mix until combined. Stir in the vanilla and lemon zest. Stir in the melted butter.
Add the flour mixture in 2-3 portions. Mix until there are still streaks of flour remaining. Stir in the blueberries, mixing just until combined.
Scoop about 1/4 cup of batter into each cup of the prepared pan. This should fill each cup almost to the top (about 3/4 full). Sprinkle the tops of each muffin with the crumb mixture.
Bake for 14-16 minutes, or until a pick inserted into the center comes out with moist crumbs. Cool in the pan on a wire rack.
Notes
*The more blueberries you use, the more muffins you’ll make. I like to use the lesser amount, and I get exactly 12 muffins with lots of crumb for each.
Store in an airtight container at room temperature for up to 4 days.