In a mixing bowl mix together the brown sugar & butter until combined.

Then add in the egg, vanilla, & milk.

Once that is all combined, add in the flour, baking soda, baking powder, & salt. Mix until the mixture is smooth.

Fold in the elderberry mixture and the blueberries.

Scoop into a greased muffin tin, filling each cup about 3/4 full.

In a small bowl mix together the 4 tbsp butter, oats, & cinnamon sugar until a crumble forms. Then sprinkle some on top of each muffin.

Bake at 350 for about 20 minutes.