3.
Making the Batter: Combine white sugar, brown sugar, salt, eggs, vanilla, and instant espresso (if using) in the bowl of a stand mixer fitted with the whisk attachment. Whip on medium-high until extremely thick and fluffy, about 8 minutes. (The whipping time can vary significantly depending on bowl size, batter temperature, and mixer wattage, so use the visual cues as your primary guide.)