Lemon Curd Shortbread Cake

This lemon bar sheet cake transforms the classic lemon bars into a delightful cake form, complete with a buttery shortbread crust, tangy lemon cake, homemade lemon curd, and creamy buttercream. The combination creates the perfect balance of sweet and tart flavors that will impress at any gathering.

I first made this cake for my sister's birthday when she requested something lemony but special. Now it has become our family's signature dessert for spring celebrations, with everyone fighting over who gets the corner pieces with extra crust.

Ingredients

• Shortbread cookies: For the crust and topping provide a buttery base that complements the tangy lemon. Look for high quality butter cookies for best flavor
• Fresh lemons: Essential for both zest and juice. Choose bright yellow lemons that feel heavy for their size, indicating more juice
• Buttermilk: Adds tenderness to the cake. Room temperature is crucial for proper mixing
• Lemon cake mix: Serves as a time saver while still allowing for customization. Duncan Hines brand yields the most consistent results
• Egg yolks: Create richness in the lemon curd. Save whites for meringue or another use
• Unsalted butter: Allows you to control salt content. European style with higher fat content produces a richer result
• Lemon extract: Enhances the citrus flavor. Optional but recommended for maximum lemon impact

Step-by-Step Instructions

Prepare the Shortbread Crust:

Process shortbread cookies until they become a fine powder, then mix with melted butter and salt. The mixture should hold together when pressed between your fingers but still remain crumbly. Press firmly into the prepared pan using a flat bottomed measuring cup to create an even layer that will hold together when sliced.

Create the Lemon Cake Layer:

Combine wet ingredients first before adding dry ingredients. The room temperature ingredients ensure proper mixing and even rising. Gently incorporate the cake mix to avoid developing too much gluten which could make the cake tough. The addition of extra flour and leavening agents helps counteract the weight of the crust.

Make Homemade Lemon Curd:

Constant stirring is essential to prevent the eggs from curdling. Watch for the magical moment when the mixture suddenly thickens around 6 minutes into cooking. Straining removes any bits of cooked egg and the lemon zest, leaving a silky smooth curd. The plastic wrap directly on the surface prevents a skin from forming.

Prepare the Lemon Buttercream:

Begin with room temperature butter for the smoothest result. Add powdered sugar gradually to achieve desired consistency. The heavy cream creates a silky texture while the extracts enhance the flavor. Whipping on high incorporates air for a lighter texture, then mixing on low removes large air bubbles for smoother piping.

Assemble the Cake:

Apply buttercream in an even layer using an offset spatula. Create decorative piping rows to form channels for the lemon curd. Fill the channels carefully with lemon curd, allowing small puddles of sunshine yellow goodness. Finish with crumbled shortbread for texture contrast and visual appeal.

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The lemon curd is truly the crown jewel of this recipe. I discovered its magic during a cooking class in culinary school where the instructor showed us how just a few simple ingredients transform into liquid gold through gentle heat and patience. My family now requests jars of this curd as holiday gifts each year.

Make Ahead Friendly

This cake works beautifully for advanced preparation. Make the lemon curd up to a week ahead and store it in an airtight container in the refrigerator. The cake itself can be baked one day ahead and kept wrapped tightly at room temperature. Assembly is best done within a few hours of serving for the freshest presentation, though the fully assembled cake will hold well in the refrigerator for up to 4 days.

Customization Options

The basic formula allows for delightful variations to suit different tastes or occasions. Try a graham cracker crust instead of shortbread for a different flavor profile. Orange or lime can substitute for lemon if you prefer different citrus notes. For a more elegant presentation, cut into individual squares and garnish each with a small edible flower or mint leaf. During holiday seasons, add festive sprinkles or colored sanding sugar to match the occasion.

Serving Suggestions

While delicious on its own, this cake pairs wonderfully with fresh berries, particularly raspberries or blueberries which complement the lemon flavor beautifully. A dollop of lightly sweetened whipped cream alongside each slice creates a lovely contrast. For a more decadent dessert, serve slightly warm with a small scoop of vanilla bean ice cream. At summer gatherings, I like to offer it with a mint infused iced tea for a refreshing combination.

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This cake brings sunshine to any gathering. Share slices with loved ones for a tangy, sweet treat everyone will adore.

Frequently Asked Questions

→ Can I make the lemon curd ahead of time?

Yes, you can make the lemon curd up to 3 days in advance. Store it in an airtight container in the refrigerator with plastic wrap pressed directly onto the surface to prevent a skin from forming. The curd needs to be cold before adding it to the cake anyway, so making it ahead is actually ideal.

→ What kind of shortbread cookies work best for the crust?

Traditional plain shortbread cookies like Walkers or Lorna Doone work perfectly. Avoid cookies with fillings or chocolate coating. You'll need enough to make 3 cups of cookie powder when pulverized, which is approximately 11-15 ounces of cookies depending on their density.

→ Can I substitute the lemon cake mix?

While Duncan Hines is recommended for best results, you can use any brand of lemon cake mix. If you can't find lemon cake mix, use a white or yellow cake mix and increase the lemon extract to 2 teaspoons, plus add the zest of an additional lemon for more citrus flavor.

→ How do I store leftovers of this cake?

Store leftovers in an airtight container in the refrigerator for up to 4-5 days. The lemon curd contains eggs and butter, so refrigeration is necessary. Allow slices to come to room temperature for about 20 minutes before serving for the best flavor and texture.

→ Can I freeze this lemon bar sheet cake?

You can freeze the baked cake layer (with crust) before adding the buttercream and curd. Wrap it tightly in plastic wrap and then foil, and freeze for up to 1 month. Thaw completely in the refrigerator before decorating. The completed cake with buttercream and curd doesn't freeze well as the textures may change upon thawing.

→ How thick should the shortbread crust be?

The shortbread crust should be about 1/4 inch thick and pressed firmly and evenly into the pan. Using the bottom of a glass or measuring cup helps create a smooth, compact layer that will hold together when the cake is sliced.