Preheat oven to 170 degrees. Line a muffin pan and set aside.
Whisk together the dry ingredients in a bowl.
Add in the buttermilk and vanilla and fold in.
Add in the butter and fold in till the mixture in moist. Finally fold in the blueberries. Do not overbeat.
Distribute equally between all the cups. Bake for 20-25 minutes till the skewer comes out clean.
Notes
I used large muffin cups and got 4 cup cakes. I baked 40 minutes for the big muffin cup. The actual recipe is double the quantity and contains one egg. So in case you are baking 12 muffins, then add an egg to the ingredients.