Can I substitute something else for the grand marnier? I'm under 21 sadly and can't get my hands on any.

i skipped the grand marnier and didn't increase OJ. it came out perfectly!

We used Cointreau for our first cake and Grand Marnier for our third. Any liqueur in the orange or cognac family, we made two without that we're delicious! Give it a sip and bite on a sliver of orange to help you decide!

I would substitute additional orange juice, along with some orange zest to add some of the more intense flavor and bitterness you would get from the liqueur.

I think you could just increase the orange juice to 1/2 cup.