Ingredients
Equipment
Method
Make the Lemon Curd
- Combine the Ingredients: In a heatproof bowl, whisk together the room-temperature eggs, granulated sugar, optional cornstarch, fresh lemon juice, and lemon zest until the mixture is smooth and evenly combined.
- Cook the Lemon Mixture: Place the bowl over a double boiler or transfer the mixture directly to a saucepan. Cook over low to medium heat, whisking constantly to prevent the eggs from curdling and to help the mixture thicken evenly.
- Thicken the Curd: Continue cooking for 15–20 minutes, whisking continuously, until the lemon curd becomes thick enough to coat the back of a spoon.
- Incorporate the Butter: Remove the curd from the heat. Gradually add the softened unsalted butter, whisking after each addition until the butter is fully incorporated and the curd looks smooth and glossy.
- Strain Until Smooth: Pass the lemon curd through a fine-mesh strainer to remove the lemon zest and any small pieces of cooked egg, leaving a silky consistency.
- Cover the Surface: Transfer the strained curd to a clean bowl or jar. Press plastic wrap directly against its surface to help prevent a skin from forming as it cools.
- Chill Completely: Refrigerate the lemon curd until it is completely cold before using it in the frosting. The curd must be fully cooled to maintain the frosting's creamy texture.
Make the Lemon Mascarpone Frosting
- Combine the Cold Ingredients: Add the cold mascarpone cheese, cold heavy cream, 80–100 g of cold lemon curd, sifted powdered sugar, and pure vanilla extract to a large mixing bowl.
- Whip Until Firm: Using a hand mixer or stand mixer, whip the ingredients on low to medium speed for approximately 2 minutes, or until the mixture becomes thick, smooth, and firm. Stop whipping as soon as stiff peaks form to avoid overwhipping.
- Frost or Fill the Desserts: Use the finished lemon mascarpone frosting immediately to decorate cupcakes, fill cake layers, or top tarts and other desserts. For neater piping and easier handling, refrigerate the frosting briefly before decorating if needed.
- Store Any Remaining Frosting: Transfer leftover frosting to an airtight container and refrigerate for up to 3 days. Keep it chilled until ready to use.
Notes
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Use cold ingredients: Keep the mascarpone cheese, heavy cream, and lemon curd cold before whipping to help the frosting achieve a smooth, stable consistency.
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Cool the lemon curd completely: Warm lemon curd can affect the texture of the frosting, so refrigerate it until fully chilled before combining it with the other ingredients.
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Adjust the lemon flavor: Use 80 g of lemon curd for a milder citrus taste or increase it to 100 g for a more pronounced lemon flavor.
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Whip carefully: Mix on low to medium speed and stop as soon as the frosting becomes thick and firm with stiff peaks. Overwhipping can compromise its smooth texture.
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Strain the lemon curd: Pass the cooked curd through a fine-mesh strainer to remove lemon zest and any small pieces of cooked egg.
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Use cornstarch if desired: The cornstarch in the lemon curd is optional and can be included as specified in the original recipe.
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Chill before piping: If the frosting feels too soft to pipe neatly, refrigerate it briefly before decorating.
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Store properly: Keep leftover frosting in an airtight container in the refrigerator for up to 3 days.
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Plan your portions: This recipe makes enough frosting to decorate approximately 10 cupcakes, fill three cake layers, or cover a 10-inch tart.