Step 1

Preheat oven to 350F. Grease two 8" or 9" round cake pans. Dust pans with flour and tap out excess any excess.

Step 2

In a large bowl whisk together flour, baking powder, baking soda, salt, and 1 1/2 cups sugar. In another bowl whisk together the melted butter, buttermilk, oil, vanilla, lemon zest, rosemary and egg yolks.

Step 3

For the meringue: In the bowl of your stand mixer fitted with whisk attachment, beat egg whites at medium speed until foamy. With machine running, stream in the remaining 1/4 cup sugar. Beat at high speed just until stiff peaks form. Gently transfer to a bowl and set aside.

Step 4

Add flour mixture to the empty stand mixer bowl fitted with whisk attachment. With mixer running at low speed, gradually pour in butter mixture and mix for about 10 seconds. Stop mixer and thoroughly scrape down the bowl. Mix again on medium for 20 more seconds just until combined.

Step 5

Using rubber spatula, gently fold in 1/2 of the meringue just until incorporated. Then fold in the rest of the meringue. Be very gentle to not deflate the air in the meringue. You will have a few white streaks in the batter. Divide batter evenly between your prepared cake pans.

Step 6

Place pans on a half-sheet pan and bake on the center rack in the oven at 350F for 20-25 minutes, rotating halfway through. The cake will begin pulling away Bake until cake layers begin to pull away from sides of pans and will no longer jiggle in the center when it is finished.

Step 7

Cool cakes in pans on wire rack for 20 minutes. Run a thin bladed knife around the sides of the pans to loosen cakes then invert on a greased wire rack. Allow to cool completely (about 1 more hour) before frosting.

Step 8

Combine all ingredients in the bowl of a stand mixer fitted with a paddle attachment. Mix on medium speed until combined and creamy. Scrape down the bowl as needed.