Preheat the oven to 400 degrees. Line 24 muffin cups with cupcake liners.

In a medium bowl combine the butter, applesauce, and sugar. Mix until well combined.

Add in the eggs and sour cream and mix well.

In another bowl combine the flour, baking powder, and salt.

Add half the egg mixture to the flour mixture and mix well. Stir in the milk and mix well. Add the remaining egg mixture and beat until just combined.

Gently fold in the blueberries and the rhubarb.

Fill the muffin cups 2/3 of the way full.

Bake for 20-25 minutes or until a toothpick inserted into the center comes out clean.