Rhubarb Streusel Muffins

Ingredients

• 1/2 cup butter, softened
• 1 cup packed brown sugar
• 1/2 cup sugar
• 1 egg
• 2 cups flour
• 1 teaspoon baking powder
• 1/2 teaspoon baking soda
• 1/8 teaspoon salt
• 1 cup (8 ounces) sour cream
• 3 cups chopped fresh or frozen rhubarb, thawed