Hi Shelley! I'm so glad you found this post helpful! In pastry school, for things like meringue-based buttercreams, we often used egg whites from containers, whereas for actual piped meringues and more "delicate" applications, we stuck with whites from freshly cracked. I think you are pretty safe to use the egg whites in a carton based on this. Perhaps you can test on a smaller scale batch to verify the brand you are buying works to be safe before making a larger batch. Hope that helps!

Forgot to leave five stars, amazing!!

Good question! For chocolate Italian meringue buttercream, you would add melted chocolate that has cooled to room temperature, but is still fluid, after making the buttercream. I would add about 175 grams of melted dark chocolate (around 1 cup) for every 4 egg whites. Hope that helps!

Thanks for posting this recipe, I will definitely be using it often! it is more than addictive and really easy to make. I had to scoop out a couple of table spoons for the rest of the family to sample and all found it extremely delicious. I made it to frost my sister's birthday cake in a couple of days and can't wait to taste it with the vanilla cake I made. I really appreciate you put such an accurate recipe mentioning quantities in grams as well as cups, I always find weighting ingredients yields more consistent results.
Just a little tip, to cut down the mixing time of egg whites when adding the hot syrup, I used a big bag of frozen peas and wrapped it around my mixing bowl while it was running. The mixture definitely cooled faster and my peas didn't melt 🙂

I forgot to answer your question about how much egg whites to use. The egg white in a large egg weighs around 30 grams, so for 10 of them, I'd use 300 grams of egg whites.

Hi Phyllis, store-bought egg whites are very convenient but most pastry chefs don't recommend using them for meringues because they don't whip up as high. Still, I think this will work, you just might not achieve the same volume and "lightness" as with freshly cracked/separated egg whites. Hope that helps!