Preheat the oven to 425 degrees F. Grease an entire standard-size muffin pan with shortening or spray with non-stick cooking spray.

Streusel

In a small bowl, rub the sugar and lemon zest between clean fingers until the lemon zest is very fragrant.

In a medium-sized bowl, mix together the lemon sugar, all-purpose flour, and cinnamon. Stir in the melted butter until well combined. Set aside.

Muffins

In a small bowl, take about 2 tablespoon of flour and toss the blueberries in the flour to coat them. Set aside.

In a medium bowl, create lemon sugar the same way as the streusel using the lemon zest and sugar amounts for the muffins. Whisk the melted butter into the lemon sugar, then add the eggs, buttermilk, and vanilla extract. Mix again until well combined.

In a large bowl, whisk the flour, baking powder, baking soda, and kosher salt together.

Add the wet ingredients to the dry ingredients bowl and gently stir using a rubber spatula until almost combined. Fold in the flour-coated blueberries until just combined, being careful not to pop them.

Divide the batter into the 12 muffin cups using an ice cream scoop, filling all the way to the top. Sprinkle the batter generously with the streusel mixture.

Bake for 5 minutes at 425 degrees F (220 degrees C), then reduce the heat to 350 degrees F (180 degrees C) and bake for another 18-20 minutes or until a toothpick inserted into the center comes out clean.

Let cool in pan on the countertop for 15 minutes. Carefully remove and transfer to a wire rack to cool.

Keep at room temperature at up to 24 hours for the best taste and texture. After that, freeze!