Preheat oven to 350°F. Line two 8-inch cake pans with parchment paper, then grease them with nonstick spray. Set aside.
In a small bowl, add 2 cups (400g) granulated sugar and the zest of a large lemon (about 1 Tbsp/6g). Use your fingertips to massage the zest into the sugar. The rubbing action releases the natural oils from the zest, intensifying the citrus flavor throughout the sugar.
Add the lemon sugar made in the step above, 2 cups + 2 Tbsp all-purpose flour (270g), 1 1/2 tsp baking powder, and 1/2 tsp fine salt in a large bowl. Use a stand mixer and paddle attachment or a hand mixer to mix on a low speed until combined.
Mix 2/3 cup (1 & 1/3 sticks or 150g) unsalted butter slowly into the dry mix, on a medium-low speed. Continue to mix until no large chunks of butter remain, and the mixture becomes crumbly.
Pour in 2/3 cup (155g) or about 5 egg whites and mix on low until just incorporated and the batter looks wet.
Then mix in 1 cup (240g) of buttermilk, 1 Tbsp of vegetable oil, 1 tsp vanilla extract, and 1 tsp lemon extract (optional) on a low speed. Scrape the sides and bottom of the bowl as needed with a rubber spatula, then beat on a medium speed for about a minute to make sure everything is properly mixed together. This also helps lighten the texture of the cake layers a bit.
Divide batter evenly between the prepared cake pans. I like to use a kitchen scale to weigh my pans and ensure they all have the same amount of batter. This guarantees your layers will bake to the same height.
Bake for 33–35 minutes, or until a toothpick comes out with a few moist crumbs. Let the cake layers cool in the pans for 10–15 minutes, then run a small offset spatula around the perimeter of each pan and carefully turn the layers onto wire racks.
Fully cool or chill the cake layers before leveling and assembling. Use a serrated knife to level the tops of the layers right before you plan to assemble your cake.