Prepare the Streusel: In a medium bowl, combine 1/2 cup of sugar, 1/2 cup of light brown sugar, and 1 cup of all-purpose flour. Pour in 1/3 cup of melted cold butter, then mix until the mixture resembles coarse crumbs. Place the bowl in the refrigerator to chill.

Make the Muffin Batter: In a large mixing bowl, beat 1/2 cup of room temperature unsalted butter until creamy. Gradually add 3/4 cup of granulated sugar, continuing to beat until light and fluffy. Mix in 2 large eggs, the zest of 1 lemon, 1/2 cup of Greek yogurt, 1/4 cup of lemon juice, and 1 teaspoon of vanilla extract until combined.

Combine Ingredients: In another bowl, whisk together 2 cups of all-purpose flour, 1 teaspoon of baking powder, and a pinch of salt. Gradually fold the dry ingredients into the wet mixture, stirring gently until just combined.

Bake the Muffins: Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or grease it. Fill each muffin cup halfway with muffin batter, add a dollop of homemade lemon curd, and top with streusel. Bake for 18-20 minutes.

Glaze the Muffins: Allow muffins to cool for 5 minutes in the tin. Mix 1 cup of powdered sugar with 2-3 tablespoons of lemon juice until smooth, then drizzle over cooled muffins.