For the Crumble Topping:
4 tablespoons unsalted butter, melted
3/4 cup all-purpose flour
1/3 cup granulated sugar
1 tablespoon lemon zest (about 1 lemon)
1/4 teaspoon salt
For the Lemon Cake:
1/2 cup unsalted butter, softened
2 tablespoons lemon zest (about 2 lemons)
1 cup granulated sugar
2 large eggs, room temperature
1 teaspoons vanilla extract
2 tablespoons fresh lemon juice (about 1 lemon)
1/2 teaspoon salt
2 teaspoons baking powder
2 cups all-purpose flour
1/2 cup sour cream
1/4 cup milk
powdered sugar for dusting, optional
Preheat oven to 325°F and grease and flour an 8-inch springform or cake pan. Line the bottom of the pan with parchment paper and set aside.
In a small bowl, make the crumble topping. Stir together the melted butter, 3/4 cup flour, 1/3 cup sugar, lemon zest, and salt. Set aside.
In a large mixing bowl, cream together the butter, sugar, and lemon zest with an electric mixer until light and fluffy.
Add the eggs, vanilla, lemon juice, salt, and baking powder and beat until combined.
On low speed, add half of the flour and mix until combined. Add sour cream and mix until combined, followed by the remaining flour, and then the milk.
Pour batter into prepared pan and sprinkle with crumble topping, leaving some larger chunks.
Bake until top is a light golden brown and a toothpick inserted into the center comes out clean, about 40 minutes.
Cool on a wire rack at least 30 minutes before serving. Dust with powdered sugar to serve, if desired.