Heavenly Italian butter cake from Pavia is cloud-light and delicately vanilla-scented. This elegant mediterranean dessert is a cherished family baking tradition.
Preheat the oven to 340°F (170°C) and butter a 9-inch round cake pan; line the base with parchment paper for easy release.
Cream the unsalted butter with powdered sugar using a stand mixer on medium speed until pale and fluffy, about 4–5 minutes.
Add eggs one at a time, beating well after each addition to ensure the batter stays light; scrape down the bowl as needed.
Sift together cake flour, potato starch, baking powder, and salt; gently fold these dry ingredients into the batter in two parts, alternating with whole milk for moisture.
Stir in vanilla extract and lemon zest, folding gently to maintain batter volume; avoid overmixing.
Transfer the batter to the prepared pan, smooth the surface, and bake for 40–45 minutes or until a toothpick comes out clean; avoid opening the oven in the first 30 minutes to retain volume.
Let the cake cool in the pan for 10 minutes, then carefully invert onto a wire rack to cool completely before serving; dust with extra powdered sugar if desired.