Good-Cooking - Sticky Rhubarb Muffins

Ingredients

• 4 tablespoons butter
• 6 tablespoons dark brown sugar
• 1 cup rhubarb, cut into small dice
• 4 tablespoons butter, softened
• 1/4 cup granulated sugar
• 1 egg
• 1 1/2 cups all-purpose flour
• 1 teaspoon baking powder
• 1/2 teaspoon baking soda
• 1/4 teaspoon salt
• 1/2 teaspoon nutmeg
• 1/2 cup milk
• Grated rind of 1 orange