To the butter mixture add ⅓ of the dry ingredients, mixing until just combined, then ½ of the wet ingredients, then repeat with the remaining ingredients ending with the dry ingredients.
I used a large ice cream scoop to add one scoop of vanilla cake batter, then a scoop of chocolate, and alternating until full. You can then use a butter knife to gently swirl the cake, sometimes
Let the marble cake cool on a wire rack for 30 minutes then I use a small angled spatula to gently release the cake from the pan then place a wire rack on top of the cake and flip over to invert the cake onto the cooling rack.