It baffles me how the videos I watch get their buttercream cakes sooo smooth.  I get smudges and lines when I got around with the icing smoother.  Do you hold the smoother directly up amd down as you turn the turntable or do you angle it a bit? Also how much pressure are you applying on the cake with the smoother? 

1st off you need a good recipe/the right consistency—have you tried this one?  

<2 of EVERYTHING ICING>      

As posted it does NOT crust but a 'fix' is mentioned at the end along with how to make it into “cream cheese”  icing :) 

Ingredients

 2 cups butter 

2 cups shortening *

2 pounds powdered sugar*

2 Tablespoons flavoring

2 generous shakes of salt shaker

 *see notes below*

DIRECTIONS:

In KA mixer (best) mix together butter and shortening on medium speed with wire whip for 8-10minutes. Add about 1/3 of the sugar; mix 5-10 minutes; add another 1/3 of the sugar, along with the flavoring, mixing 5 minutes; add the remaining sugar and mix on low 10 minutes until smooth.

There is NO liquid needed in this recipe.    

Want this icing to crust? Reduce either the butter OR the shortening by 1 cup OR reduce *both* by 1/2 cup

*NOTES*:

*I have always used salted butter—but unsalted is good if you prefer. And even with the change in  shortenings a few yrs back I still use Crisco; any good brand hi-ratio will probably be better.  

* Flavorings can be *ANY!* combination you want. What I used mostly is: 1 part vanilla; 1/2 part butter flavoring and 1/4 part almond. A "Part" can be any measure you want. Do you make many, manyr cakes? Mix it up by the cupfull, pint or even gallon:)  OR if for only one cake/icing use teaspoons as the 'part'/measure.

• for an even stiffer icing that dries even more add up to 1 cup  more powdered sugar
• For a shelf stable cream cheese tasting version simply add 2 Tablespoons of white balsamic vinegar with the 2nd addition of sugar.  (that tip comes from another baker friend(K8 Memphis) 

I prefer to apply the icing w/the Wilton quick icer tip, then smooth w/the small off-set spatula.  If that doesn’t do it the bench scraper comes out, hold it straight up & down, & turn the turntable.   Any problem *still* there wait for it to crust well & use a Viva paper towel    I know that seems like a lot but I seldom need any more than the off set &.or bench scraper.  

Have a few pix somewhere... I’ll see if I can find them & post for you tomorrow 

I set the bottom edge of my bench scraper flat against the turntable so the sides will be perfectly straight, from top to bottom.  I reach around the turntable as far as possible so I can make one full revolution without moving the scraper, removing only a small amount of frosting with each revolution.  It takes time and practice and as kakeladi said, a good, smooth frosting.

although they don't crust, meringue icing and 'cooked flour' aka ermine icings are much easier to smooth -- but for regular buttercream you can use different techniques too -- after smoothing, spray water on it, then smooth again using a small spatula and working up and down or whatever -- watch the water doesn't accumulate at the bottom, use a smaller stand underneath like a can of beans or something -- not my favorite method but some like it --

there's a hot knife (spatula) method, dip spatula in hot water, dry it off each time to re-smooth over imperfections --

there's an upside down technique probably on you tube or on here -- some people use a paint roller -- some people place a smooth paper towel and rub a fondant smoother over that -- or you can just press a thickly folded smooth weave cloth towel onto areas that need smoothing -- that's what I do if necessary --

if you get bubbles on the surface of your smoothing, run your spatula the other way --

 lynniepoo -- thanks for the honorable mention in your famous icing recipe -- so sweet!!!

sniff sniff 

I forgot to add, I do hold the bench scraper at a 45 degree angle to the side of the cake, not at 90 degrees sticking straight out from the cake.  I also dip my scraper in hot water, then dry it off, near the end of the process.  

Any of those methods do work ... but I have found using the small off-set spatula with my icing recipe needs little smoothing it’s so easy to work with.  Now maybe it just that I’ve had so many yrs experience:)  

All of the above. 

I agree, meringue buttercream is the easyest to smooth. If you're more an abc type, you must try kakelady's 2 of everything recipe. A charm to smooth and delicious. Whatever the recipe you choose, always beat it a long time and slow with the paddle. It helps avoid air bubble, that's the key.

and i seem to recall someone using a torch on their spatula to heat it -- but pretty sure if i tried that i would get black scorch transferred to my cake -- and there you have a new way to make black icing...potentially jk jk jk jk jk jk

but not about the torch