I tried out a new "buttercream" frosting recipe to try for a super smooth surface and it worked great! Here's the recipe (from here):
1 cup Crisco (or other quality vegetable shortening)
1/2 cup (stick) of butter, (allowed to come to room temperature)
1 tsp clear vanilla flavor (clear so that your buttercreams soft yellow color isnt compromised)
1 tsp of flavoring such as crème bouquet or lemon (optional) (I'd add extra butter flavoring)
1/4 cup milk (more or less as needed for consistency desired)
1 pinch salt (for use with unsalted butter only)
1 tsp meringue powder
2 lb bag of powdered (confectioners) sugar that has been sifted
On lowest speed, incorporate the these last three ingredients, just until they’ve begun to combine, and then turn the mixer up to medium speed, and blend until smooth and a little fluffy. If using a stand-up mixer, this texture will achieved after about 2 minutes, and if using a hand-held mixer, after about 5 minutes.
If while you’re mixing, the mixer beings to strain or you notice the icing is too stiff, add more water or milk, very small amounts at a time until you have the consistency you want. If the mixture becomes too soft, then simply add more powdered sugar.
And the best tip they gave to get that perfectly smooth top - Paper towels!! And not just any - they have to be Viva since Viva doesn't have a textured pattern on there. Once you've frosted the cake and let it sit for 15-30min or until it's "crusted" then you place your paper towel on there and start gently rubbing with your hand. Works like a charm!