Preheat oven to 375°F. Line a 12 cup muffin tin with liners or spray with baking spray. Set aside. Toss blueberries with 1 Tbsp flour. Set aside.
In a medium size mixing bowl, use a whisk to sift together 2 cups flour, sugar, baking powder and salt.
In a separate bowl, whisk together buttermilk, oil, eggs and vanilla until fully combined.
Add wet ingredients to dry mixing by hand using a whisk or with an electric mixer, until combined. Fold in blueberries by hand.
Use an ice cream scoop or a ¼ cup measuring cup to divide the batter evenly into each muffin tin cup.
To make the crumble topping: Cut butter into sugar, oats and flour with a fork or a pastry blender until it resembles peas. Sprinkle evenly over the batter in each cup.
Bake for 25-30 minutes or until a toothpick inserted into the center comes back clean.
Cool in the pan for 5 minutes then remove to a cooling rack to cool completely.
Store in an airtight container chilled or at room temperature for up to 3 days.