Adapted from Rose Levy Beranbaum's Rose's Heavenly Cakes
Makes 2 cups
- 3 large egg yolks, or 3-1/2 tablespoons
- 1/4 cup plus 2 tablespoons superfine sugar
- 1/4 cup (2 fluid ounces) golden syrup or light corn syrup
- 1 teaspoon lemon juice, freshly squeezed
- 16 tablespoons (2 sticks) unsalted butter
- 1 teaspoon pure vanilla extract
- 1/3 cup seedless raspberry or strawberry preserves (alternatively, you can use 1/2 cup of fresh raspberries or strawberries, pureed in a food processor)
Step 1: To beat the egg yolks: Have ready a 1-cup heatproof glass measure, lightly coated with nonstick cooking spray.
Step 2: In a medium bowl, with an electric mixer, beat the yolks until light in color.
Step 3: Meanwhile, in a small saucepan, preferably nonstick, combine the sugar, golden syrup, and lemon juice.
Step 4: Using a silicone spatula, stir until all the sugar is moistened. Heat over medium-high, stirring constantly, until the sugar dissolves and the syrup begins to boil around the edges. Stop stirring and continue cooking for a few minutes, until the syrup comes to a rolling boil. (The entire surface will be covered with large bubbles.) Immediately transfer the syrup to the glass measure to stop the cooking.
Step 5: To complete the buttercream: If using a stand mixer fitted with the whisk beater, with the mixer turned off, pour a small amount of syrup over the yolks. Immediately beat on high speed for 5 seconds. Stop the mixer and add a larger amount of syrup. Beat on high speed for 5 seconds. Continue with the remaining syrup. For the last addition, use a silicone spatula to remove the syrup clinging to the glass measure and scrape it off against the beater. Continue beating for 5 minutes.
Step 6: Allow to cool completely. To speed cooling, place the bowl in an ice water bath or in the refrigerator, stirring occasionally.
Step 7: When cool, beat in the butter 1 tablespoon at a time on medium speed. The buttercream will not thicken until almost all of the butter has been added.
Step 8: Add the vanilla and raspberry preserves, if using, and beat on low speed until incorporated. Place the buttercream in an airtight bowl. Use it at once (it will have a slight crunch until it stands for several hours) or up to 4 hours later. If you are keeping it longer, refrigerate it and bring it to room temperature before using. To restore its texture, rebeat it, but not until it has reached room temperature, in order to avoid curdling