Mix-In Muffins

Ingredients

• 1 1/2 c all-purpose flour
• 1/3 c sugar
• 1 1/2 tsp baking powder
• 1/4 tsp baking soda
• 1/4 tsp salt
• 1 stick butter, unsalted
• 1 c sour cream
• 1 large egg
• 1 tsp vanilla