In a medium bowl, whisk the flour, baking powder, baking soda, and salt together until combined. Set aside.
2 1/2 cups All-purpose flour, 2 tsp Baking powder, 1/2 tsp Baking soda, 1 tsp Kosher salt
In a large bowl, combine the sugar and lemon zest. Using your fingers, rub the zest into the sugar until combined. Rubbing the lemon zest into the sugar helps release the oils in the zest and infuses more lemon flavor.
1 cup Granulated sugar, Zest 2 Large Lemons
Whisk the eggs into the sugar mixture until they’re thick, about 1 minute. Slowly whisk in the melted and cooled butter until combined. Whisk in the buttermilk, lemon juice, and lemon extract until combined.
2 large Eggs, 1/2 cup Unsalted butter, 3/4 cup Buttermilk, 1 tsp Lemon extract, 1/4 cup Lemon juice
Using a spatula, fold the dry ingredients into the wet ingredients just until combined. Do not overmix. Let the batter rest for 15 minutes while you preheat the oven to 425ºF. (The muffin batter will thicken upon resting.)
Divide the batter equally into the muffin cups. Sprinkle each muffin with about 1 1/2 tablespoons of streusel. Bake for 5 minutes at 425ºF, then reduce the oven temperature to 350ºF and bake for an additional 12-15 minutes or until a toothpick inserted into the center of a muffin comes out clean; do not overbake. Let the muffins cool in the pan for about 5 minutes, and transfer to a wire rack to cool completely.