Preheat oven to 350º. Line a baking pan (or two if needed) with paper liners, or grease with cooking spray.
Prepare the streusel topping according to instructions below. (set aside)
In a separate small mixing bowl, whisk together flour, baking powder and salt and set aside.
In a large mixing bowl or mixer, whisk together butter and sugar until light and fluffy. Add eggs, vanilla, milk, lemon juice, lemon zest, and continue whisking until smooth. Fold in flour mixture with a rubber spatula until just combined.
In a small mixing bowl, toss blueberries with 3 Tbsp. flour until blueberries are coated. Use a slotted spoon to remove blueberries and shake off any excess flour.
Fold the blueberries into the muffin batter.
Fill muffin cups about 3/4 full of batter and sprinkle each cup of batter with about 1 Tbsp. streusel topping.
Bake at 350º for 20 to 25 min, until a toothpick inserted into the center of a muffin comes out clean.
Let muffins cool for a few minutes in the muffin pan before removing to cool on a wire rack. Serve immediately or store in a sealed container.