Instructions

Note: French buttercream requires some attention to detail. It is possible that you might need to make it a few times before you master it. If this is your first time making it, consider making a small batch so you don't risk wasting so many eggs. 

1. Place the sugar and water in a saucepan over medium heat with a candy thermometer. Bring the temperature up to 240 F.
2. Meanwhile, in the bowl of a stand mixer fit with a whip attachment, whip the egg yolks until light and fluffy. This should take about 3-4 minutes on medium/high speed while the sugar syrup is heating.
3. With the mixer still running, carefully pour the sugar syrup into the mixing bowl. Make sure you pour it on the edge of the bowl and let it stream down the side into the egg yolks. Do not pour it right into the egg yolks or this could cause them to cook unevenly and leave you with chunks of egg yolks.
4. Turn the mixer up to high and whip at high speed until the mixing bowl is cool to the touch on the bottom.
5. Mix in the vanilla and the salt. With the mixer running, add the butter one piece at a time until the piece is absorbed before adding the next.
6. Use immediately or store covered in the refrigerator for up to 3 days. Re-whip the frosting before using if you stored it.

*This is enough buttercream to frost about 24 cupcakes, or to fill a 4 layer 8" cake or a 3 layer 9 or 10" cake. It is also enough frosting to cover the top of a 9x13" sheet cake. This frosting doesn't work well as the main frosting for a layer cake. It is too soft and unstable.