Preheat the oven to 350°.
Spray a muffin tin.
Add in a tiny pat of butter to each muffin form (overall about 2 TBSP) and top with ½ tsp of brown sugar in each one.
Add about 10 blueberries to each muffin form.
Combine cake mix, 1 egg, 4 tbsp of melted butter and buttermilk.
Scoop about 2 TBSP of the cake mix and add it to the top of the blueberries in the muffin forms.
Bake 25-30 min.
Let them cool for about 20 min. Run a knife along the edge of each one and turn the pan over onto a cooling rack.
Enjoy alone or with a scoop of ice cream!