- Place the egg yolks in a bowl. Set aside.
- In a small saucepan over high heat, dissolve the sugar in half of the water (1/4 cup/60 ml). Cook without stirring until the caramel becomes light amber in colour. Remove from the heat. Add the remaining water (1/4 cup/60 ml) and the corn syrup. Beware of splattering. Return the saucepan to the heat and let simmer until a candy thermometer reads 242°F (117°C).
- Beat the egg yolks with an electric mixer at medium speed. Drizzle the hot caramel onto the yolks, avoiding the mixer’s beaters. Beat continuously at high speed until completely cooled.
- Add the butter, 1 or 2 pieces at a time, beating until smooth and creamy. With a spatula, scrape the bottom and sides of the bowl several times during this step.
Can be made in advance, just bring to room temperature and beat before using.