Preheat oven to 400 degrees. Lightly grease 18-20 muffin cups or add cupcake liners.

In a large mixing bowl, whisk together the flour, salt, baking powder, baking soda and ¾ cup of granulated sugar. Make a well in the center.

In a small mixing bowl, combine the sour cream, melted butter, vanilla, lemon zest and lemon juice. Add the lightly beaten eggs and fold together until blended using a rubber spatula. Add the sour cream mixture to the flour and sugar. Stir until the dry ingredients are moistened. Gently fold in the blueberries. Spoon the batter into the prepared muffin tins, filling each about three-fourths full. Allow the muffins to rest at room temperature for 15 minutes before baking or topping with the crumble mixture.

While the muffins are resting, prepare the crumble topping. Melt butter in a small bowl in the microwave. Add the flour, sugar, and lemon zest. Mix with a fork to combine. Sprinkle the topping (leaving some pieces in larger clumps) evenly on top of the unbaked muffins.

Bake the muffins at 400°F for 18 minutes or until golden brown. Cool the muffins in the pan on a rack for 5 minutes, then remove to a wire rack to cool.

While muffins cool, combine powdered sugar and lemon juice. Drizzle over muffins and serve.