Tangy Lemon Bar Slab with Buttery Shortbread Base

Why You’ll Love This Recipe

• Crisp, buttery shortbread base that actually snaps—not soggy.
• Bright, tangy lemon-curd custard with just the right sweet-tart balance.
• Clean, bakery-style squares thanks to smart cooling and cutting tips.
• Big-batch slab feeds a crowd, perfect for parties, bake sales, and potlucks.

Grocery List

• Produce: 5–6 large lemons (for 1 cup juice + zest)
• Dairy: 1 cup unsalted butter; 6 large eggs + 2 yolks
• Pantry: All-purpose flour, granulated sugar, powdered sugar, vanilla extract, fine sea salt

Full Ingredients

Shortbread Base

• 1 cup (226 g) unsalted butter, melted and slightly cooled
• 2 cups (240 g) all-purpose flour
• 1/2 cup (60 g) powdered sugar
• 2 tbsp (25 g) granulated sugar
• 1/2 tsp fine sea salt
• 1 tsp vanilla extract

Tangy Lemon-Curd Custard

• 6 large eggs + 2 large egg yolks (at room temperature)
• 1 3/4 cups (350 g) granulated sugar
• 1 cup (240 ml) fresh lemon juice (from about 5–6 lemons)
• 2 tbsp finely grated lemon zest
• 1/4 cup (30 g) all-purpose flour
• Pinch fine sea salt

To Finish

• Powdered sugar, for dusting (about 1/2 cup or to taste)

Step-by-Step Instructions

Step 1: Prep the pan and preheat

Position a rack in the center of the oven and heat to 350°F (175°C). Line a 9×13-inch metal baking pan with parchment so it overhangs on the long sides for easy lifting. Lightly mist or butter the pan to help the parchment stick.

Step 2: Make the shortbread base

In a medium bowl, whisk together the flour, powdered sugar, granulated sugar, and salt. Stir in the melted butter and vanilla until a soft, sandy dough forms. Crumble the dough into the prepared pan, then press it into an even, compact layer, taking care to firmly pack the corners and edges. Dock all over with a fork to minimize bubbling.

Step 3: Bake the crust until crisp-edged

Bake at 350°F (175°C) for 18–22 minutes, until the edges are lightly golden and the surface looks set and matte. Remove the pan, reduce the oven temperature to 325°F (165°C), and keep the crust warm while you finish the filling.

Step 4: Whisk the lemon-curd custard

In a large bowl, rub the sugar and lemon zest together with your fingertips until the sugar is fragrant and pale yellow—this releases the oils for deeper lemon flavor. Whisk in the eggs and yolks until smooth but not foamy. Whisk in the lemon juice, then the flour and a pinch of salt until fully incorporated. For the silkiest texture, strain the mixture through a fine-mesh sieve into a large measuring cup or pitcher.

Step 5: Bake the custard on the hot crust

Carefully pour the filling over the hot crust. Bake at 325°F (165°C) for 20–25 minutes, until the edges are set and the center has a slight, even wobble when the pan is gently nudged. If the center appears liquid or sloshes, continue baking in 2-minute increments. Avoid overbaking to keep the custard tender and bright.

Step 6: Cool, chill, and finish

Transfer the pan to a rack and cool at room temperature for 1 hour. Refrigerate uncovered for at least 2 hours (or up to overnight) to fully set. Dust generously with powdered sugar just before cutting—sift for an even, snowy finish.

Step 7: Trim and cut neat squares

Use the parchment to lift the slab onto a cutting board. Trim 1/8–1/4 inch from the edges for the cleanest presentation. Use a long, sharp knife to cut 24 bars (6 rows by 4 columns), wiping and rinsing the blade between cuts for crisp edges.

Pro Tips

• For brighter flavor, zest directly over the sugar so escaping citrus oils land where they matter—then rub in well.
• Strain the filling to remove bubbles and any bits of egg or zest for a custard that sets luxuriously smooth.
• Pour the filling onto the crust while it’s still hot; this helps the layers adhere and prevents separation.
• Don’t overbake: look for a uniform jiggle, not a liquid center or a stiff, cracked top.
• Powdered sugar dissolves on moist surfaces—dust right before serving for a pristine look.

Variations

• Meyer Lemon Bars: Use 1 cup Meyer lemon juice and reduce sugar in the filling to 1 1/2 cups (300 g) to keep the sweet-tart balance.
• Almond Shortbread: Swap 1/2 cup (56 g) of the crust flour for almond flour and add 1/4 tsp almond extract for a nutty twist.
• Lime or Grapefruit: Substitute equal amounts of lime or pink grapefruit juice and zest; adjust sugar to taste depending on fruit sweetness.

Storage & Make-Ahead

Refrigerate bars in a single layer (or stacked with parchment between layers) in an airtight container for up to 5 days. For best appearance, dust with powdered sugar just before serving. To freeze, wrap the chilled, uncut slab tightly or freeze cut bars on a sheet until firm, then store in a freezer bag for up to 2 months; thaw overnight in the fridge and dust before serving. You can bake the crust a day ahead, cool, cover, and hold at room temperature; add the filling and bake the next day.

Nutrition (per serving)

Approximate per bar (1 of 24): 220 calories; 9 g fat; 31 g carbohydrates; 3 g protein; 120 mg sodium; 21 g sugars. Nutrition is an estimate and will vary with exact ingredients and dusting amount.