• Line a 9-inch springform pan with parchment paper. Set aside and preheat the oven to 350 degrees Fahrenheit (180 degrees Celsius).

Make the Streusel

• Whisk flour, sugar, and lemon zest together in a small bowl. Pour in the melted butter and mix with a fork until pea-sized pieces form. Cover and place in the refrigerator while you make the cake batter.
  75 grams all purpose flour, 120 grams granulated sugar, 1 teaspoon lemon zest, 70 grams unsalted butter

Make the Cake

• Place the sugar in the bowl of a stand mixer or electric mixer. Zest the lemons into the sugar and use your fingers to rub them together until it turns yellow with a sandy texture, creating lemon sugar. Juice the lemons immediately after into a separate bowl. You need 5 tablespoons of juice total.
  333 grams granulated sugar, 2 tablespoons lemon zest
• Add softened butter to the lemon sugar and beat on medium-high speed for 2-3 minutes. The mixture should be light and fluffy.
  376 grams unsalted butter
• Add the eggs one at a time, mixing on low speed until well incorporated. Scrape the bottom and sides of the bowl with a rubber spatula, then beat in the sour cream, vanilla extract, and lemon juice. It's normal if it looks curdled.
  5 large eggs, 200 grams sour cream, 2 teaspoons vanilla extract, 3 tablespoons fresh lemon juice
• Add the flour, baking powder, and salt. Mix in the dry ingredients on low speed until the white streaks of flour just blend into the batter. Do not overmix.
  396 grams all purpose flour, 1 ½ teaspoons baking powder, 1 teaspoon salt
• Pour the batter into the lined pan. Sprinkle the streusel on top (it might be firm from being in the fridge- break it up with a fork or other utensil if so). Then bake for 50 minutes-1 hour or until a toothpick inserted in the center comes out clean with a few moist crumbs attached. The edges of the cake may have pulled away from the pan slightly and the crumb should be golden brown.
• Remove from the oven and let the cake cool in the pan for 5-10 minutes. Release the pan and carefully transfer the cake to a wire rack to cool completely for about 30 minutes.

Make the Icing

• Once the cake is completely cool, whisk powdered sugar and lemon juice together in a medium bowl until smooth.
  120 grams powdered sugar, 2 tablespoons fresh lemon juice
• Drizzle the glaze on top of the cake, slice, and enjoy!