I made this recipe for s’mores cupcakes https://www.marthastewart.com/314199/marshmallow-frosting

I didn’t have cream of tartar so I used a tsp of lemon juice.  Also, I didn’t use any extra t cuz I didn’t have vanilla and thought almond might taste weird with the s’mores cupcakes.  The recipe says to put eggs and everything in the mixer bowl then heat.  Thought that was strange but did it anyway.  Cooked til sugar dissolved, temp was about 125. Took it off and mixed with KA.  It took WAY longer to set up, like over 15 min on high.  The bowl was warm up until then.  Finally got it close to stiff peaks, piped, and then used broiler to toast.  Broiler also warmed up the cupcakes themselves as well.  While piping, it seemed to loose its “stiffness” (for lack of better word).  It had a faint egg flavor prior to broiling and more so after.  I refrigerated a cupcake and after coming back to room temp it has different consistency and more egg flavor.  

suggestions?  Customer is picking up the cupcakes tomorrow afternoon.  I could probably whip up another batch and redecorate tomorrow morning.  

For now I would replace the icing.

I didn't read the recipe but I would suggest that the eggs were heated too high and cooked them which imparts an eggy flavour that otherwise isn't detectable.

yes what bubs said

I agree with replacing the icing.  Since it is a s'mores cupcake and you want a marshmallow frosting, why not try a recipe that calls for marshmallow fluff?  Basically it would be a basic buttercream with fluff added to it (here is one I found after doing a quick google search...https://www.aprettylifeinthesuburbs.com/marshmallow-vanilla-buttercream-frosting/   ).  You won't be able to torch it the same way as you would an actual marshmallow frosting but you can garnish the cupcake with a piece of graham cracker, a piece of chocolate, and a torched marshmallow to give you that s'mores look.

Replace the icing and go get some vanilla extract before you do.  That's literally the only flavoring in it; you can't skip it.  Otherwise, you get what you got, which is sweet egg whites. Then again, I've always found plain meringues (like on lemon pie) to be very eggy so that may be just me. But really, go get the vanilla.

Do you guys think 125 is too high?  I've never made this kind of marshmallow frosting but doesn't the meringue for SMBC go as high as 165? 

yes it should go higher -- but then some people use uncooked egg whites like duff so who knows

Uncooked??  Oh, I'm going to have to go look up more about his cakes and frostings. 

I was question the temp too, Every recipe I found for marshmallow frosting said 120.  I thought that they had to be to 165 as well. 

I think it’s the toasting that’s giving it the egg flavor.  Probably cuz I’m cooking the eggs lol.  Tried another batch with vanilla and got the same result.  I added some marshmallow fluff to the frosting and it took a bit of the egg flavor away and I could still toast it.  Next time I’m trying the marshmallow fluff BC.  Thanks for the advice! 

149 farenheit of 65 celcius. The trick is to keep stirring it (although some people don't and still get good results) as if you don't whisk while heating the eggs heat unevenly and you risk cooking the egg white on the bottom before it all comes to temp, trust me you will regret not just whisking it if that happens lol.

Find a good marshmallow recipe that uses gelatin instead of egg and you won't have an egg flavor. Also, you cannot skip the vanilla flavoring or it just won't taste right no matter what recipe you use.

Personally, the best MMF fondant I've ever tried, and only use, is the one by Liz Marek, LMF. Google that and try her recipe. It tastes amazing and you don't have to use any ingredients like gelatin or eggs. I've never had it mess up on me and everyone who I make it for absolutely loves it. No one peels the fondant off lol.

LMF is fantastic to work with, and taste so much better than commercial fondant.  it's a good 'doctored' mix.

Just to agree with the other people posting.  The heat of the water is important in cooking up the egg/sugar mixture.  If the water is boiling it's too hot .  Just a low simmer & sometimes when I lift up the pan to peek at the water...…...if it's got too many bubbles in the simmer I turn the heat  down.  

Low & slow heating is best. .

I'd just use your normal buttercream recipe and add marshmallow creme to it to get the marshmallow flavor. I use the same buttercream recipe for everything and just adjust the flavor accordingly to what I am using it for.

I don't think you'd be able to torch that, though.

Update - I did replace the original frosting.  The second batch turned out much better.  I did use the vanilla this time.  I also added marshmallow fluff to inhance the flavor.  I used a torch instead of the broiler.  All that combined - it turned out great!! On a side note, I had saved leftover of the first batch and refrigerated.  After a day it had all separated!  White fluff on top, egg whites in the bottom.  Bleh!  Glad I switch out to the second batch.  Thanks again for the info everyone!