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This sheet cake puts a fun spin on traditional lemon bars, featuring a rich buttery crust, zingy lemon cake, tangy homemade curd, and smooth frosting. It strikes just the right balance between sweet and tart that'll make your guests ask for seconds.
I whipped this up for my sister when she wanted a special lemony treat on her birthday. It's now become what our family looks forward to every spring, and everyone fights to grab those corner pieces with the extra crunchy crust.
Ingredients
- Shortbread cookies: They create that buttery foundation and garnish. Go for quality butter cookies to get the tastiest results
- Fresh lemons: You'll need both the zest and juice. Pick ones that are sunny yellow and feel hefty, as they'll give you more juice
- Buttermilk: Makes your cake super soft. Don't forget to let it sit out until it hits room temp for the best mixing
- Lemon cake mix: A handy shortcut that still lets you add your personal touch. I've found Duncan Hines works most reliably
- Egg yolks: They add that lovely richness to your curd. You can save the whites for something else
- Unsalted butter: Lets you manage how salty things get. Try European styles with extra fat for an even tastier outcome
- Lemon extract: Kicks up that citrus punch. You can skip it, but I'd suggest keeping it in for maximum lemon flavor
Step-by-Step Instructions
- Prepare the Shortbread Crust:
- Grind those cookies into fine crumbs, then mix in the melted butter and salt. When you squeeze it, the mix should stick together but still feel a bit crumbly. Push it firmly into your pan using a flat-bottomed measuring cup to make a nice even layer that won't fall apart when you cut it later.
- Create the Lemon Cake Layer:
- Start by mixing all the wet stuff before you add the dry ingredients. Using room temp ingredients helps everything blend properly and rise evenly. Don't overmix when you add the cake mix or you'll end up with a tough cake. We add extra flour and leaveners to support the weight of that crust below.
- Make Homemade Lemon Curd:
- Keep stirring non-stop to stop the eggs from cooking too quickly. You'll know it's done when it suddenly thickens up around the 6-minute mark. Run it through a strainer to get out any cooked egg bits and zest, leaving you with a perfectly smooth curd. Put plastic wrap right on the surface to keep a skin from forming.
- Prepare the Lemon Buttercream:
- Your butter needs to be soft for the best results. Add the powdered sugar bit by bit until you get the texture you want. The heavy cream makes it extra smooth, while those extracts pump up the flavor. Whip it on high speed to get it fluffy, then switch to low to work out big air bubbles for prettier piping.
- Assemble the Cake:
- Spread your buttercream evenly with an offset spatula. Pipe rows to make little valleys for the lemon curd. Carefully fill those valleys with the curd, making little pools of bright yellow goodness. Finish by sprinkling crumbled shortbread on top for a nice crunch and pretty look.
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That lemon curd really steals the show in this dessert. I learned the technique during a cooking class where the teacher showed us how a few simple things can turn into something amazing with gentle heat and a bit of patience. My relatives now beg for jars of this stuff as Christmas presents.
Prep Ahead Tips
This dessert is great for planning ahead. You can make your lemon curd up to a week early and keep it in a sealed container in the fridge. The cake layer works fine baked a day before and wrapped well at room temp. Try to put everything together within a few hours of when you'll serve it for the freshest look, though the whole assembled cake stays good in the fridge for up to 4 days.
Customization Options
You can switch things up easily to match what you like. Try using graham crackers instead of shortbread for the crust. Switch lemon for orange or lime if you want different citrus flavors. For fancy events, cut it into small squares and top each with a tiny edible flower or mint leaf. During holidays, add some festive sprinkles or colored sugar that matches the season.
Serving Suggestions
This cake tastes amazing by itself, but it's even better with some fresh berries, especially raspberries or blueberries that go so well with lemon. A spoonful of lightly sweetened whipped cream next to each slice looks and tastes fantastic. If you want something extra special, serve it slightly warm with a small scoop of vanilla bean ice cream. At summer parties, I love to pair it with mint iced tea for a super refreshing combo.
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This dessert brings brightness to every occasion. It's the perfect tangy treat to share with friends and family who'll absolutely love it.
Frequently Asked Questions
- → Can I make the lemon curd ahead of time?
You can definitely prep the lemon filling up to 3 days early. Just keep it in a sealed container in your fridge with plastic wrap touching the surface so it doesn't form a skin. The filling needs to be cold when you add it to the cake anyway, so making it beforehand works great.
- → What kind of shortbread cookies work best for the crust?
Plain shortbread cookies like Walkers or Lorna Doone are your best bet. Don't use cookies with fillings or chocolate. You'll need enough to make 3 cups of cookie crumbs when crushed, roughly 11-15 ounces depending on how dense the cookies are.
- → Can I substitute the lemon cake mix?
Duncan Hines works best, but any lemon cake mix brand will do. If you can't find lemon cake mix anywhere, grab a white or yellow mix and add 2 teaspoons of lemon extract plus the zest from an extra lemon to pump up the citrus taste.
- → How do I store leftovers of this cake?
Keep any leftover cake in a sealed container in your fridge for up to 5 days. Since the lemon filling has eggs and butter, you can't leave it out. Take slices out about 20 minutes before eating so they can warm up a bit for the tastiest experience.
- → Can I freeze this lemon bar sheet cake?
You can freeze the cake part with the crust before adding frosting and filling. Just wrap it really well in plastic wrap and then foil, and it'll keep for a month in the freezer. Let it thaw completely in your fridge before decorating. The finished cake with frosting and filling doesn't freeze well because the texture gets weird when it thaws.
- → How thick should the shortbread crust be?
Your shortbread base should be about 1/4 inch thick, pressed down firmly and evenly in the pan. Using a flat-bottomed glass or measuring cup really helps make a smooth, tight layer that won't fall apart when you cut the cake.