Heat oven to 375 degrees. In a medium saucepan over medium heat melt the butter. Then add the brown sugar. Melt together for about 3 minutes and then set aside to cool for about 5 minutes.
Then line 24-30 muffin tins with muffin cup liners.
In a bowl mix together flour, baking soda, baking powder, and salt. Mix together and set aside
In a large mixing bowl add the eggs and sour cream. Beat together. Then once the butter and brown sugar mixture is cooled slowly add that into the egg and sour cream mixture. Stir in the oats. Then fold in the flour mixture. Then fold in the blueberr.
Fill the muffin tins about three-quarters full and then sprinkle a generous pinch of sugar on top of each muffin.
Bake for 24-26 minutes or until the edges are medium brown and the tops are firm.