1-Preheat oven to 400 F degrees and: Preheat oven to 400 F degrees and line standard muffin or cupcake pan with paper liners and set aside.
2-To make the crumb topping in a: To make the crumb topping in a small bowl, whisk together flour, sugar and cinnamon, add melted butter and stir with a fork until crumbly. Refrigerate until ready to use.
3-To make the muffins in large bowl: To make the muffins in large bowl stir together flour, baking powder and salt and set aside.
4-In a medium bowl place 2/3 cup: In a medium bowl place 2/3 cup granulated sugar and lemon zest and rub for a minute. Add eggs and whisk together eggs and lemon-sugar until combined. Whisk in yogurt, oil, lemon juice and vanilla extract (mixture should be pale and yellow).
5-Fold wet ingredients into dry ingredients and: Fold wet ingredients into dry ingredients and whisk everything together.
6-Reserve ½ cup of blueberries for topping: Reserve ½ cup of blueberries for topping. Place remaining blueberries in a small bowl. Dust blueberries with 1 tablespoon flour and toss them until all blueberries are coated with thin layer of flour and then fold them really gently in the batter.
7-Spoon batter into prepared muffin tins, filling: Spoon batter into prepared muffin tins, filling maximum 2/3 of each cup and gently tap the pan on the work surface to set. Cover the batter with the remaining blueberries and then cover the blueberries generously with streusel topping.
8-Place them in the oven and bake: Place them in the oven and bake at 400 F for 5 minutes, then REDUCE THE OVEN TEMPERATURE TO 375 F and bake 13-15 minutes or until the toothpick inserted in the center comes out clean.
9-Cool for 5 minutes in the pan: Cool for 5 minutes in the pan then remove muffins and cool on a wire rack.