Crumb Cake Muffins

Ingredients

• 3/4 cup packed brown sugar
• 2 teaspoons ground cinnamon
• 1/2 cup unsalted butter, melted
• 1 1/2 cups all-purpose flour
• 1 teaspoon baking powder
• 1/2 teaspoon baking soda
• 1/2 teaspoon salt
• 1/2 cup unsalted butter, softened
• 3/4 cup granulated sugar
• 2 large eggs, at room temperature
• 3/4 cup sour cream or plain yogurt
• 1 teaspoon pure vanilla extract
• 2 Tablespoons milk
• 1 cup confectioners sugar
• 2-3 Tablespoons milk or heavy cream