1/2 cup unsalted butter (1 stick), room temperature, plus more for pan
1 1/2 cups all-purpose flour (spooned and leveled), plus more for pan
1/2 pound lemons (about 2), ends removed, cut crosswise into thin slices, and seeds removed
1/4 cup fresh lemon juice (from 1 lemon)
1 1/2 teaspoons baking powder
1/2 teaspoon baking soda
1 cup granulated sugar
2 large eggs
1/2 cup buttermilk
1 teaspoon pure vanilla extract
Confectioners’ sugar, for dusting
Raspberries and whipped cream (optional), for serving
Preheat oven to 350 degrees. Lightly butter and flour a 9-inch round cake pan (2 inches deep). In a medium saucepan, cover lemon slices with 3 cups water. Add pinch of salt, cover, and bring to a boil over high.
Boil lemons, partially covered, until very tender, 15 minutes.
Drain in a colander and transfer to a food processor, along with lemon juice; process until smooth. Set aside.
In a small bowl, whisk together flour, baking powder, baking soda, and 1/2 teaspoon salt. In a large bowl, using an electric mixer, beat butter on medium, 2 minutes.
Gradually add granulated sugar and continue to beat until light and fluffy, 3 to 4 minutes, scraping down bowl as needed. Add eggs, one at a time, beating after each addition.
With mixer on low, gradually add flour mixture in 3 additions, alternating with 2 additions buttermilk. Beat in vanilla, then fold in lemon mixture.
Transfer batter to pan and bake until deep golden brown and a toothpick inserted in center comes out with a few moist crumbs attached, 35 to 40 minutes.
Let cool in pan on a wire rack, 20 minutes. Remove cake from pan and let cool completely on rack. Dust with confectioners’ sugar and serve with raspberries and cream, if desired