For topping combine all ingredients, using fingers to incorporate butter into pea sized crumbs. Set aside.
For the muffins, whisk together the egg, milk, vanilla, and butter. In a large bowl whisk together the remaining dry ingredients. Add in the egg mixture, stirring until just combined, then fold in ¾ cup of the blueberries.
Drop batter into paper lined muffin tins to 2/3 full, and top with 1 Tbsp or so of the crumble mixture. Top with a few of the reserved blueberries.
Bake at 375°F for 25-30 minutes.