Hello!  I am a novice baker, decorator.   I am trying to do a birthday cake for my son.  Last year I made a large 2 layer square cake...it didn't bake even, couldn't get it even,  my icing would kind of squish out between layers causing a bulge.  Used basic icing Wilton recipe but added  baking margarine in it  (package said great for baking) with shortening.    I would like to know a good icing for decorating that holds up well that is not sickingly sweet.     I really only try do this 2 or so times a year simply because family seems to prefer regular cakes (adults).  This birthday will take place in a park, so I won't have a fridge to store it in for couple or so hours.  Advice?  Thanks

Wiltons recipe for buttercream is ok but you can cut back the sugar to make it less sweet. What size cake are you planning to make?

Thanks for responding.  He would like a building shaped cake to put 2 Marvel heroes battling on top.  I know I will be stacking the cakes and they need to be even.  Was thinking like a single 9X13 base, then maybe 2 to4  8 inch circle stacked.   It is amazing all of the icing recipes you find on the internet.   Would just like a good one that works and tastes good. Even with those bake strips you put on pans, I still get a bump in the middle.         

Here is a link to my trial run on buttercream from scratch, hope it helps! buttercream Recipe.

Baking margarine was probably not the best choice for the frosting. 

You don't mention if you are aware of the support you will need for stacking. You will need support between the rounds and the 9x13, and for every 4" of height of the rounds.

look up Indydebi, sugar shack, bunny mock shack, or charlottes whipped bc recipes. They will work well for you. Get your hands on a pound or two of hi ratio shortening. This will be even better. Bakers Nook sells it by the individual pound. You can cut with butter, for better taste but the more you do, the heat stability will diminish. If you are not putting in enough flavoring, or too much flavoring, no matter what recipe you use it won't be very tasty. But then, every body has different tastes.

if there's a cake top bulge, you have to trim it. Some recipies can handle flattening with a smaller cardboard cake round and a small soup can right out of the oven. Some recipies you cannot squish like this. 

chill the cake completely before traveling. Box it up and seal the box. Leave in the box at the park for as long as you can. If you've got a cooler big enough, place box in the cooler with ice, keep ice away from soaking the box.

After pouring batter in my pans, before they go in the oven, I give them a good spin.  Centrifugal force makes sure the batter gets to the edges and corners.  I don't need to do quite so much leveling after they come out of the oven.

^^^ love that!  Sounds both practical and entertaining :)

Thanks for all of your replies.  Guess I will get a cake leveler thing then to trim.  Will check  those icing recipes too! Maybe can choose a good one :)