Preheat the oven to 375º and line a muffin pan with liners or grease it well.
Cream together the melted butter and sugar. Add in the milk, vanilla, eggs and sour cream. Whisk together until combined.
In a seperate bowl, combine the flour, baking powder, baking soda and salt. Add the dry ingredients to the wet ingredients and combine. Do not over mix! Add the sprinkles and fold in.
Scoop the batter into the muffin tins and fill them almost completely (about 7/8 full). Bake in the preheated oven for 18-20 minutes.