Preheat your oven to 350 degrees F and lightly grease an 8-inch cake pan. Consider lining it with parchment paper for easy removal.
Sift together flour, baking powder, and salt in a medium bowl.
In a large bowl, beat sugar, butter, and oil until light and fluffy. Add egg yolks one at a time, then stir in vanilla extract and lemon zest.
Gradually add dry ingredients to the sugar mixture, alternating with lemon juice and milk. Stir until the batter is smooth.
In a separate bowl, whip egg whites until stiff peaks form. Gently fold them into the batter.
Pour the batter into the prepared cake pan, smoothing the top with a spoon or spatula.
Bake for 40 to 45 minutes or until a toothpick inserted in the center comes out clean.
Allow the cake to cool in the pan before removing. Let it cool completely for optimal results.
