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