Preheat the oven to 350º.

Whisk together the flour, baking powder, baking soda, and salt in a medium bowl.

Whisk together the butter, olive oil, and sugar in a large bowl until combined. Add the eggs and whisk for 1 to 2 minutes, until lightened in color. Add the vanilla, buttermilk, lemon zest and juice, and whisk to combine. Add the flour mixture and whisk to combine.

Spray 2 8-inch round cake pans with baking spray with flour. Divide the batter evenly between the prepared pans. Tap the pans a few times each on a kitchen towel on your countertop to level the surface and remove air bubbles from within the batter.

Bake for 28 to 32 minutes or until a toothpick inserted into the center comes out with only a few crumbs. Transfer to a cooling rack. Let cool in the pans for 10 minutes, then turn out onto a cooling rack to cool completely, about 1 1/2 hours.

Add the butter, cream cheese, and lemon zest to the bowl of an electric stand mixer fitted with the paddle attachment and beat on medium speed until creamy, about 2 minutes. Add the powdered sugar and beat on low speed until combined. Increase the speed to medium and beat until smooth, about 1 minute. Scrape down the sides and bottom of the bowl. Add the lemon juice and yellow food coloring, if using. Beat until light and smooth, about 2 more minutes.

Trim the cake layers to make the tops flat and even, as needed. Place 1 cake layer on a cake plate. Spread 1 cup of buttercream over top. Top with the second cake layer and spread buttercream all over the top and sides of the cake.

Garnish with white chocolate curls, lemon slices, and/or edible flowers, if desired.