1Mix cornstarch and 1 Tbsp of water. In a saucepan, bring blueberries, sugar, and water to a boil. Simmer for 10 minutes, stir in cornstarch mix, and cool.
2Mix flour, sugar, and salt. Add diced butter and mix with fingers until crumbly. Set aside.
3Preheat oven to 375°F. Mix sugar + lemon zest. Beat in butter until light. Add eggs one at a time, then vanilla.
4In a separate bowl, sift flour, salt, and baking powder. Alternate adding dry ingredients and milk to the butter mixture. Fold in blueberries.
5Line a 12-cup muffin tin with liners. Fill with batter, drizzle with blueberry syrup, and sprinkle crumble.
6Bake at 375°F for 30-35 minutes or until golden brown.