Make Crumb Topping:
Prepare crumb topping: In a small bowl, combine 1 cup (125g) flour, 1/2 cup (100g) sugar, and 1/2 teaspoon cinnamon. Pour in 6.5 tablespoons (92g) melted butter and mix with a fork until crumbs form. Chill until needed.Whisk Dry Ingredients:
Make muffin batter: In a large bowl, whisk 1 1/2 cups (188g) flour, 2 teaspoons baking powder, and 1/4 teaspoon salt. Set aside.Mix Wet Ingredients:
In a medium bowl, rub 2/3 cup (133g) sugar with 1 tablespoon lemon zest for 1 minute. Whisk in 2 eggs. Add 2/3 cup (160g) Greek yogurt, 1/3 cup (80ml) vegetable oil, 2 tablespoons (30ml) lemon juice, and 1 teaspoon vanilla; whisk until pale yellow.Combine Wet and Dry:
Pour wet mixture into dry ingredients and fold until just combined.Toss Blueberries with Flour:
Put remaining blueberries (around 1 cup) in a small bowl. Toss with 1 tablespoon (8g) flour. Gently fold coated berries into batter.Fill Cups and Add Topping:
Divide batter among muffin cups, filling each about 2/3 full. Tap pan on counter to level. Top with reserved 1/2 cup blueberries, then sprinkle generously with crumb topping.Bake Muffins:
Bake at 400°F (205°C) for 5 minutes. Reduce oven to 375°F (190°C) and bake 13-15 minutes more, until a toothpick inserted in center comes out clean.Cool Muffins:
Let muffins cool in pan for 5 minutes, then transfer to a wire rack to cool completely.