Makes about 1 cup
125 grams (4½ ounces or 1 stick + 1 tablespoon) unsalted butter, softened
70 grams (2½ ounces or 5 tablespoons) granulated sugar
2 tablespoons water
3 egg yolk at room temperature
2 teaspoons key lime juice
1 teaspoon key lime rind
Green food coloring (preferably paste)
Beat the butter until smooth.
In a separate bowl, beat the egg yolks with an electric mixer until thick and foamy.
Combine the sugar and water in a small saucepan and boil to the soft ball stage (238°F). Very gradually add the syrup to the egg mixture in a thin stream, beating rapidly between each addition. Beat with an electric mixer until thick and fluffy and room temperature. Beat in the butter, a tablespoon at a time. If the mixture looks curdled keep beating at high speed. If it gets soupy, refrigerate for about 15 minutes and beat again. Finally beat in the food coloring, then the lime juice a drop at a time and finally stir in the lime rind. Refrigerate until firm enough to pipe.
Recipe Copyright by Michael Krondl