• Preheat oven to 350 degrees. Grease two 9-inch-wide by 2-inch-high round cake pans and line bottoms with parchment paper. Dust with flour.
• Whisk flour, baking powder, baking soda, salt, and only 1 ½ cups sugar together in large mixing bowl or in the bowl of a stand mixer. bowl. Reserve the remaining ¼ cup of sugar for the whites.
• Whisk melted butter, buttermilk, oil, vanilla, and yolks in another bowl (or a 4 cup liquid measure).
• Begin beating dry ingredients at low speed with the mixer. Gradually pour in butter/yolk/oil mixture and mix until almost incorporated (a few streaks of dry flour will remain), about 15 seconds. Stop mixer and scrape whisk and sides of bowl. Return mixer to medium-low speed and beat until smooth and fully incorporated, 10 to 15 seconds.
• Beat egg whites until foamy. Gradually add remaining ¼ cup sugar and beat until stiff peaks just barely start to form -- they don't need to be dry.
• Using rubber scraper, stir ⅓ of whites into batter to lighten, then add remaining whites and gently fold into batter until no white streaks remain. Divide batter evenly between prepared cake pans. Lightly tap pans against counter 2 or 3 times to dislodge any large air bubbles.
• Bake for 20 to 22 minutes (up to 27) or until cakes appear set and are beginning to pull away from sides of pan. Let cakes cool on wire rack for 10 minutes. Loosen cakes and invert.

Milk Chocolate Frosting

• Melt the milk chocolate in the microwave using 50% power and stirring every 30 seconds to 1 minute. Let it cool.
• In the bowl of a food processor, process butter, sugar, cocoa powder and salt until smooth. Add corn syrup and vanilla and pulse until smooth, then scrape sides of the bowl and add chocolate. Process until smooth and creamy. Ice the cake immediately.