Place a rack in the upper third of the oven and preheat oven to 375 degrees F. Line a muffins pan with paper or foil liners, set aside.
To make the muffins: Melt butter in a small saucepan over medium heat. Keep an eye on the butter. It will melt, froth, and begin to crackle. That’s the water cooking out of the butter. The crackling will subside and butter will begin to brown fairly quickly. Remove from heat when butter solids become a medium brown color and butter smells slightly nutty. Immediately pour hot butter into a small bowl, or the butter will continue to cook in the hot pan. Allow to cool slightly.
In a medium bowl, whisk together milk, egg, yolk, and vanilla until combined. Add browned butter and whisk to combine.
Whisk together flour, sugar, baking powder, and salt in a medium bowl. Add milk mixture all at once to the flour mixture and stir gently to combine. Gently but thoroughly fold in the lemon zest, poppy seeds, and blueberries. Divide batter among prepared muffin cups.
To make the topping: Combine all ingredients in a bowl and rub together with clean fingertips until crumbly. Sprinkle topping evenly over the muffin batter in cups.
Bake muffins 16 to 20 minutes until golden and crisp and a skewer inserted into the center of a muffin comes out clean. Cool muffins in the pan for 15 minutes before removing. Serve warm or at room temperature.
Muffins will last, at room temperature in an airtight container, for up to 3 days. These muffins also freeze well.
source: Joy The Baker
I used Frozen Huckleberries and the tartness of the berry along with the sweet crumb topping is delicious. Blueberries or Raspberries would also work perfectly.