13 egg yolks
2 cups of sugar
1 cup of light Karo syrup
3 pounds unsalted butter
1 cup Hershey's Cocoa
Cook's note: This incredible mousse can be used for frosting a cake or a filling for cream puffs.
Beat egg yolks until light and fluffy (mixture should look like whipped cream). Set aside. Place in a heavy pot the sugar and Karo syrup. Mix over medium heat and bring to a slow boil, stirring frequently about 12-15 minutes. (Do not hard boil this mixture as it will either burn or caramelize.) After about 12 minutes, begin checking syrup by dipping a spoon into it and allowing the syrup to run off; when syrup begins to string, it is ready to be added to the beaten egg yolks. With mixer running at a very low speed, gently pour syrup into beaten egg yolk.
When adding hot syrup, try not to pour it too close to beaters. After syrup is incorporated into egg yolk, continue beating at a higher speed for at least 10 minutes, allowing mixture to cool somewhat.
Cut butter into 1 tablespoon portions and begin adding 3-4 at a time until all butter is incorporated into egg and syrup mixture. After this step, mousse should be very creamy.
Slowly add the cocoa, mixing until well blended. Once this is finished, you are ready to frost a cake or fill cream puffs.
Source: Toni Saad Moore