1. Preheat oven to 425° F. 
2. With a fork, break up the first four topping ingredients into large pea-size pieces, then mix in milk. Set aside. 
3. Using a hand mixer, cream butter and sugar until light and fluffy. Now, beat in egg and vanilla. 
4. In a separate bowl, whisk together flour*, salt, and baking powder.
5. Add dry mixture and buttermilk to wet ingredients, a little at a time, until batter comes together.
6. Gently mix blueberries with remaining flour and sugar, then fold them into batter. 
7. Add batter to greased muffin pan and sprinkle with topping.
8. Bake until the tops are golden and a toothpick comes out clean, about 20–25 minutes.
9. Let cool on wire rack for 5 minutes before loosening with a knife and carefully remove from the muffin pan. 
10. Cool to room temperature on a wire rack before serving.

*Tip: For lighter muffins substitute cake flour for AP flour.