Eggs – Royal icing safety concern

First of all, it is extremely rare for the yolk of an egg to become contaminated if the egg is reasonably fresh. Contamination only tends to occur when the egg is quite old and the yolk membrane weakens. (Source)

Now, that said, egg yolks begin to set at a temperature of 62° C (144° F), and salmonella can be killed at temperatures as low as 59° C (138° F), so it actually is possible to "cook" the yolk sufficiently to kill any bacteria without letting it set, but you have a very small window to work with, so you need to be careful. If the temperature is even 1° too low, you'll just be encouraging the spread of more bacteria, and if it's even 1° too high, you'll ruin your recipe because the yolk will set.

Nevertheless, if you have a reliable, uniform heat source, you could attempt to heat the egg to 60-61° C for about 1 minute.

Unfortunately, you won't be able to use the technique used in other recipes - such as Bavarian cream - of simply using the residual heat of the other wet ingredients to cook the yolk sufficiently for safety while not allowing sufficient time to set. Dark chocolate is the most heat-resistant but will easily burn at temperatures significantly above 50° C (125° F). Mixing the chocolate with cream may raise this temperature slightly, and I admit to not being certain of the exact amount, but I'm pretty sure it won't get you up to the required 59° C - and it really actually needs to be much higher than that because the temperature must stay that high for several seconds after adding the eggs.

So my advice to you is to either:

• Pre-cook the yolks very carefully to a temperature just below 62° C (use a thermometer!); or
• Use very fresh eggs from a reliable source; or
• Don't eat mousse made with egg yolks, if you can't tolerate the (very low) risk.

The ingredients they post are:

• 1 cup solid vegetable shortening
• 1 teaspoon Wilton Flavor (vanilla, almond or butter)
• 7-8 teaspoons milk or water
• 1 lb. confectioners' sugar
• 1 tablespoon Meringue Powder
• pinch of salt (optional)

I would make the following suggestions based on these ingredients:

• It's not really butter cream icing if you're using vegetable shortening. You'll get far superior flavour by using butter. Pure butter may have trouble holding its shape, but you should have no trouble at all switching to a half-and-half mixture. This ratio won't change the colour much either.

• I've never personally cared for the Wilton flavourings and suspect that is a major part of the problem here. If you're using the vanilla, it's not real vanilla, it's imitation vanilla extract; pure vanilla extract is dark brown and would colour the icing. Their almond flavour also seems to taste nothing like normal almond extract, and the butter flavour is thoroughly pointless (just use butter!).

  You can use real vanilla extract, but it will definitely darken the icing. You can try to compensate with an icing whitener, but those things are intended for slightly-off-white icings and probably won't get you all the way to white. Alternatively, you can use pure almond extract instead of the imitation; it is actually clear to begin with.

  Or, better yet, you can just change your brand. Lorann makes a bunch of concentrated flavouring oils that might taste less fake. If you go to any baking supply store you'll probably see other brands as well. Try a few until you find one that you like.

• You don't say whether you're using milk or water, but use whole milk or even cream if you can; don't miss an opportunity to lay on the fat (and therefore flavour).

• Finally, a lot of people (me, for example) find the taste of meringue powder to be disgusting. You don't need it, and the vast majority of buttercream icing recipes don't contain it.

  If you really want a meringue-based buttercream, as opposed to a simple buttercream without any egg products at all, then just go for broke and make it from an Italian meringue; whip some egg whites to soft peaks, then whip boiling sugar syrup into the eggs until the mixture stiffens, and afterward incorporate the butter and other flavourings.

  I know, they're going to tell you that it won't be stiff enough. But stabilizing a meringue is dead easy; just bloom some gelatin in the cold liquid (water/milk/cream) before you incorporate it¹. The more gelatin, the stiffer it will get. Don't overdo it because if you add too much gelatin, you won't even be able to get it out of the bag (this has happened to me). A 1% ratio should be plenty.

Making a great-tasting decorating icing is easy. Stiffness isn't usually the problem, colour is. If you want brilliant white icing then you have to make certain tradeoffs. If you're willing to settle for a cream colour (or slightly whiter, with a whitener) then you've got nothing to worry about.

_{1. If you're not starting with a hot meringue, then be sure to heat the liquid with bloomed gelatin to dissolve before adding it to the icing!}