– 2 packages vanilla cake mix – 2 large eggs – ⅔ cup vegetable oil – 1 cup granulated sugar – ¼ cup cornstarch – 1 ½ cups water – 3 egg yolks – 1 tablespoon lemon zest – ¼ cup lemon juice – 1 tablespoon salted butter – ½ cup powdered sugar – 1-2 tablespoons whole milk or cream