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This sheet cake takes the beloved lemon bar and transforms it into a cake masterpiece, featuring a rich buttery shortbread base, zesty lemon cake, tangy homemade curd, and smooth buttercream. It's got that perfect sweet-tart balance that'll wow everyone at your next get-together.
I whipped this up for my sister on her birthday when she wanted something lemony but extra special. These days it's become our go-to spring celebration dessert, and there's always a friendly battle over who gets those corner slices with the extra crust.
Ingredients
- Shortbread cookies: They create that wonderful buttery foundation and topping. Go for premium butter cookies to get the tastiest results
- Fresh lemons: You'll need both the zest and juice. Pick bright, hefty lemons as they'll give you more juice
- Buttermilk: This makes your cake super tender. Don't forget to let it warm to room temp before 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: These bring a lovely richness to your curd. The whites can be saved for another dish
- Unsalted butter: This lets you manage how salty your cake is. The European kinds with extra fat make everything taste better
- Lemon extract: It boosts that citrus punch. You can skip it, but it really brings out the lemon flavor
Step-by-Step Instructions
- Prepare the Shortbread Crust:
- Grind those cookies into fine crumbs, then mix them with melted butter and salt. Your mix should stick together when squeezed but remain somewhat crumbly. Pack it down firmly in your pan using a flat measuring cup to make an even layer that won't fall apart when you cut it later.
- Create the Lemon Cake Layer:
- Start by mixing all wet stuff first, then add your dry ingredients. Make sure everything's at room temp so it blends properly and rises evenly. Don't overmix once 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.
- Make Homemade Lemon Curd:
- Keep stirring non-stop to keep those eggs from cooking too fast. You'll notice it suddenly thicken about 6 minutes in, that's your magic moment. Run it through a strainer to catch any egg bits and zest, leaving you with super smooth curd. Put plastic wrap right on the surface so it doesn't form a skin.
- Prepare the Lemon Buttercream:
- Your butter needs to be soft but not melty. Add powdered sugar bit by bit until you like how thick it is. The heavy cream makes it silky while the extracts pump up the flavor. Beat it on high to get it fluffy, then switch to low to knock out big air bubbles for smoother decorating.
- Assemble the Cake:
- Spread that buttercream evenly with your offset spatula. Pipe decorative rows to make little valleys for the lemon curd. Carefully fill those valleys with sunny yellow curd, letting it pool slightly. Sprinkle crumbled shortbread on top for a nice crunch and pretty finish.
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That lemon curd is really the star of the show here. I learned how to make it during a cooking class back in culinary school where our teacher showed us how a few simple things turn into something magical with just gentle heat and a little patience. My family now asks for jars of this stuff as gifts every holiday season.
Make Ahead Friendly
This dessert is great for planning ahead. You can whip up the lemon curd as far as a week before and keep it in the fridge in a sealed container. The cake part can be baked a day early and left wrapped up tight at room temp. It's best to put everything together within a few hours of when you'll serve it, but the finished cake stays good in the fridge for up to 4 days.
Customization Options
There are lots of ways to switch things up with this basic idea. Try using graham crackers instead of shortbread for the crust if you want a different taste. You can swap the lemon for orange or lime if that's more your thing. For fancy occasions, cut it into little squares and top each one with a tiny edible flower or mint leaf. During holidays, throw on some festive sprinkles or colored sugar to match the celebration.
Serving Suggestions
This cake tastes amazing by itself, but it's even better with some fresh berries on the side, especially raspberries or blueberries that really complement the lemon flavor. A small spoonful of lightly sweetened whipped cream makes a nice contrast with each slice. If you want something more indulgent, serve it slightly warm with a scoop of vanilla bean ice cream. At summer parties, I like to pair it with mint iced tea for a super refreshing combo.
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This cake brings a ray of sunshine to any table. Share it with friends and family for a zingy, sweet experience that'll have everyone asking for seconds.
Frequently Asked Questions
- → Can I make the lemon filling beforehand?
Absolutely, you can whip up the lemon filling up to 3 days early. 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 put it on the cake anyway, so making it ahead works really well.
- → What shortbread cookies should I use for the bottom?
Plain shortbread cookies like Walkers or Lorna Doone are your best bet. Don't use any with filling or chocolate on them. You'll need enough to make 3 cups of crushed cookies, which is about 11-15 ounces depending on how dense they are.
- → Can I use a different 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 one extra lemon to boost that citrus kick.
- → How do I keep leftover cake fresh?
Put any leftovers in a sealed container in your fridge for up to 4-5 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 aren't too cold - they taste way better at room temp.
- → Can I freeze this cake?
You can freeze the baked cake part with the crust before adding any toppings. Wrap it really well in plastic and then foil, and it'll keep for up to a month in the freezer. Let it thaw completely in your fridge before adding the frosting and filling. Don't try freezing the finished cake though - it'll get weird when it thaws out.
- → How thin should I make the shortbread base?
Your shortbread base should be around 1/4 inch thick, pressed down firmly all over the pan. Using a glass bottom or measuring cup helps you get a nice, even layer that won't fall apart when you cut the cake later.