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1
Put a rack in the upper third of the oven and preheat oven to 350 degrees F. Line muffin pan with paper or foil liners.
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2
Melt butter in a small saucepan over medium heat. Keep an eye on the butter. Melt and cook down the butter until little brown bits appear in the pan. The crackling will subside and butter will begin to brown fairly quickly after that. Keep a close eye. Remove from heat.
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3
If using vanilla bean, split the vanilla bean down the center, scrape the seeds out, and in a small bowl, rub the vanilla beans into the granulated sugar. I used my fingers and it worked like a charm. Set aside.
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4
In a medium bowl, whisk together milk, eggs, and vanilla. Add the brown butter and stir to combine.
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5
In a large bowl, whisk together flour, sugar, baking powder and salt in a medium bowl Add milk and butter mixture all at once, and stir gently to combine.
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6
Divide half of the batter among muffin cups. Stir the espresso and water mixture into the remaining batter. Divide the espresso batter between the twelve muffin cups.
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7
To make the topping combine all of the ingredients in a bowl and rub together with your fingertips until crumbly. Sprinkle evenly over the batter in the cups.
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8
Bake until golden and crisp and a wooden pick inserted into the center of a muffin comes out clean, about 18-20 minutes. Keep an eye on them they dry out quickly. Cool in pan on a rack for 15 minutes then remove from the pan. Serve warm or at room temperature.
