Preheat the oven to 350°F (180°C). Grease a 9-inch round cake pan with butter, dust it with flour, and tap out the excess.
In a large bowl, beat the eggs and sugar with an electric mixer on high speed for 5–7 minutes, until the mixture is pale, triples in volume, and is very fluffy.
Reduce the mixer speed to low. Add the vegetable oil, milk, and lemon zest, and mix just until combined.
In another bowl, sift together the flour, baking powder, and salt.
Fold the dry ingredients into the wet ingredients in 2–3 additions using a rubber spatula, working from the bottom up and stopping as soon as the flour is incorporated.
Pour the batter into the prepared pan and gently tap the pan on the countertop to release any large air bubbles.
Bake for 30–35 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake rest in the pan for 10 minutes. Then run a knife around the edge, turn the cake out onto a wire rack, and let it cool completely before slicing.