• 1/3 cup sugar (2 1/4 ounces)
• 1/3 cup dark brown sugar (2 1/2 ounces)
• 3/4 teaspoon ground cinnamon

• 1/8 teaspoon table salt
• 8 tablespoons unsalted butter, melted but warm
• 1 3/4 cup cake flour (7 ounces)

• 1 1/4 cup cake flour (5 ounces)
• 1/2 cup sugar (3 1/2 ounces)
• 1/4 teaspoon baking soda
• 1/4 teaspoon table salt
• 6 tablespoons unsalted butter, cut into 6 pieces, softened but still cool

• 1 large egg
• 1 large egg yolk
• 1 teaspoon vanilla extract
• 1/3 cup buttermilk

For the topping, whisk sugars, cinnamon, salt and warm melted butter in a medium bowl. Add flour and stir with a rubber spatula or wooden spoon until it comes together as a dough. Set aside at room temperature to cool.

For the muffins, heat oven to 325° and position the rack in the upper-middle part of the oven. Line standard-sized muffin tins with baking liners. In the bowl of a stand mixer, combine flour, sugar, baking soda and salt on low speed to combine. Add butter one piece at a time and beat until mixture resembles moist crumbs and butter has been incorporated, about 2 minutes. Add egg, yolk, vanilla and buttermilk. Beat on medium-high speed until light and fluffy, about 1 minute.

Use a 1/4 cup measuring cup or scoop to divide batter evenly among muffin cups and even out the tops with a spatula. The muffin tins should be half full. Break the crumb mixture into large pea sized pieces and spread in an even layer over the smoothed tops of each muffin to cover. This should fill the muffin tins. Bake about 20 minutes or until a toothpick comes out clean and crumbs are golden. Transfer to a wire rack and cool at least 20 minutes.