Coffee cake muffins

Ingredients Crumbs 1/2 cup all-purpose flour 1/4 cup granulated sugar 1/2 teaspoons ground cinnamon 1/8 teaspoon salt 1/4 cup unsalted butter, melted Cinnamon swirl 1/3 cup granulated sugar 1 1/2 teaspoons ground cinnamon Muffin 3 cups all-purpose flour 3 teaspoons baking powder 1/2 teaspoon ground cinnamon 1/2 teaspoon salt 1/2 cup unsalted butter, at room temperature 1 cup granulated sugar 1/4 cup light brown sugar, packed 2 large eggs plus 1 egg yolk, at room temperature 1 and 1/2 teaspoons vanilla extract 1 1/2 cup of Buttermilk Glaze 1 cup confectioners' sugar, sifted 2 to 3 Tablespoons buttermilk 1 teaspoon vanilla extract a pinch of salt . For the Buttery Crumb Topping: 2. In a medium mixing bowl, combine the flour, sugar, cinnamon, and salt. Stir in the room temperature butter, mixing just until combined. Set aside while you prepare the rest of the recipe. The mixture will absorb the butter as it sits and become more crumbly by the time you’re ready to use it. 3. For the Cinnamon Sugar Layer: 4. In a small mixing bowl, combine the sugar and cinnamon. Set aside. 5. For the Muffins: 6. Preheat oven to 400°F (204°C). Line a 12 cup muffin tin with paper liners and set it aside. 7. In a large mixing bowl, combine the flour, baking powder, cinnamon, and salt. Set aside. 8. In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using a handheld electric mixer, combine the butter and both sugars and beat on medium-low speed until light and fluffy; about 3 minutes. Add in the eggs and yolk, one at a time, beating well after each addition. Slowly beat in the vanilla, buttermilk, and sour cream. Reduce mixer speed to low and gradually add in the dry ingredients, mixing just until combined. Be sure not to over mix here. 9. For the Glaze: 10. In a small mixing bowl, whisk together the confectioners' sugar, buttermilk, vanilla, and salt until smooth. Add more confectioners' sugar to thicken or more buttermilk to thin.