I got the recipe from the Cake Mix Doctor. It was the lemon-lime cake with pineapple curd and I adapted it somewhat. The lemon lime filling for the 7UP cake I got on here from amycake and I posted it under “fillings” here.
Again, it doesn’t make the cake taste so much like “7UP” but it gives it something extra that makes it really special!
Place a rack in the center of the oven and preheat the oven to 350 degrees farenheit. Grease and flour your pans – the cake mix dr. calls for 3 9 in round cake pans, but I found it only made 6 cups of batter so choose pans that will work with 6 cups. (See Wilton for batter amounts for certain pans)
Place the cake mix, pudding mix, eggs, oil, and root beer in a large mixing bowl. Blend w/ an electric mixer on low speed for 1 minutes. Stop and scrape down sides. Increase speed to medium and beat 2 to 3 more minutes. Batter should look well combined & thickned.
I then made the crusting buttercream icing from this website – the one that uses butter & Crisco. For the lemon flavor, I just added a little bit of lemon juice in place of the vanilla.