For the Muffins:
10 tablespoons (140 g) unsalted butter
1/2 cup plus 2 tablespoons (270 g) whole milk
2 large eggs
2 teaspoon (7 g) vanilla extract
2 ¼ cups (315 g) Cup4Cup flour
1 cup (200 g) granulated sugar
2 ¼ teaspoons (7 g) baking powder
1 teaspoon (5 g) kosher salt
1 tablespoon instant espresso powder mixed with 3 tablespoons warm water
For the Topping:
3 tablespoons (42 g) cold, unsalted butter, cut into ½-inch cubes
½ cup (70 g) Cup4Cup flour
3 ½ tablespoons (44 g) granulated sugar
½ teaspoon (1 g) ground cinnamon
1. Preheat oven to 350°F.
2. Line a muffin pan with paper muffin liners.
3. Melt butter in a small saucepan over medium heat. Once melted, heat over medium-high heat to make brown butter. Cook until little brown bits appear in the bottom of the pan and it smells nutty. Immediately, remove pan from the heat. Pour brown butter into a heat proof bowl.
4. In a medium bowl, whisk together milk, eggs, and vanilla.
5. In a large bowl, whisk together flour, sugar, baking powder and salt. Add milk mixture and brown butter. Stir gently to combine. Batter will be thick.
6. Divide the batter into two bowls. Stir the espresso and water mixture into one of the bowls. You now have 2 batters. Scoop the plain batter into the prepared muffin tin, dividing it evenly. Next, scoop the espresso batter on top of the plain batter.
7. To make the topping combine all of the ingredients in a bowl and rub the butter in between your fingertips until it becomes fully incorporated. The mixture should be crumbly. Sprinkle evenly over the batter in the muffin pan.
8. Bake until muffins are golden, crisp and the muffins spring back when pressed firmly, about 20-25 minutes. Cool in pan on a rack for 15 minutes then remove from the pan.