– You need a siphon/kidde to make a foam. The ones from ISSI I like the best.
Bring the gastrique and salt to a boil.
Using a hand blender, mix in the egg yolks, being careful not to get scrambled eggs. How to do this. Keep in constant motion.
When your yolks are nicely incorporated continue with your whisk. Keep whisking until you get a nice thick and bound sauce. If it goes too fast and threatens to burn, remove your pan from the heat and keep tapping.
When you have a nice shiny thick sauce, slowly add the beure noisette. Tap it all together well once more.
Fill your siphon and aerate with two cartridges. Shake well and your foam is ready to use. This froth is most delicious lukewarm or at room temperature.