Shortbread Recipe

Prepare and blind-bake crust

Preheat oven to 350°F (175°C). Lightly grease an 8x8-inch (or 9-inch) square baking pan and line with parchment paper, leaving an overhang for easy removal. In a large bowl, combine 2 cups flour, 1/2 cup granulated sugar, 1/4 tsp salt and 1 tablespoon lemon zest; whisk to distribute. Add 1 cup cold cubed unsalted butter. Using a pastry cutter or your fingertips, cut the butter into the dry ingredients until the mixture resembles coarse crumbs with some pea-sized pieces remaining. Press the mixture evenly and firmly into the bottom of the prepared pan, smoothing the top with the back of a measuring cup or your fingers so the crust is even (about 1/2 inch thick). Prick the surface a few times with a fork to prevent large bubbles.

Bake the crust on the middle rack for 20–25 minutes, or until edges are just turning golden. Remove from the oven and let cool slightly while you prepare the lemon curd. Keep the oven on (you will briefly return the assembled bars to set the meringue).

Cook lemon curd

In a medium heatproof bowl, whisk together 1/2 cup fresh lemon juice, 1/2 cup granulated sugar, 3 egg yolks and 1 whole egg until smooth and slightly pale. If using, whisk in 1 teaspoon lemon zest. Set the bowl over a saucepan of barely simmering water (double boiler), ensuring the bottom of the bowl does not touch the water. Stir constantly with a spatula or whisk as the mixture gently thickens — about 8–10 minutes — until it coats the back of the spatula and reaches about 170–175°F (77–80°C) if using a thermometer.

Remove the bowl from heat and immediately whisk in 4 tablespoons cold butter, piece by piece, until fully incorporated and the curd is glossy and smooth. If there are any small lumps, strain the curd through a fine-mesh sieve into a clean bowl. Allow the curd to cool 5 minutes, then pour it evenly over the baked shortbread crust and spread to the edges. Return to the oven for 5 minutes to help the curd set slightly. Remove and cool on a wire rack for 15–20 minutes.

Make Swiss-style meringue

While the curd cools, combine 3 room-temperature egg whites, 1/2 cup granulated sugar and 1/4 teaspoon cream of tartar in a heatproof bowl (or the bowl of a stand mixer). Place the bowl over a saucepan of simmering water and whisk constantly until the sugar has dissolved and the mixture feels warm to the touch (about 130°F/54°C) and no longer grainy when rubbed between fingers — roughly 3–4 minutes.

Transfer the warm egg-white mixture to a stand mixer fitted with the whisk attachment (or use a hand mixer). Whip on medium-high speed until glossy stiff peaks form and the bowl has cooled to near room temperature, 5–7 minutes. Add 1/2 teaspoon vanilla extract in the last 30 seconds and beat to incorporate.

Using a spatula or piping bag, spread or pipe the meringue over the cooled lemon curd, making decorative peaks. Optionally sprinkle 1 teaspoon sanding sugar over the tops for extra sparkle.

Return the assembled bars to the oven at 325°F (160°C) for 6–8 minutes, or until the meringue tops are set and just starting to color at the peaks. Alternatively, for a toasted finish, use a kitchen torch to gently brown the meringue peaks to your liking. Remove from the oven and cool completely on a rack (at least 30 minutes) so the curd sets fully.

Once cooled, use the parchment overhang to lift the shortbread from the pan and transfer to a cutting board. With a sharp knife wiped between cuts, slice into 9 or 12 squares. Store leftover bars in an airtight container in the refrigerator for up to 4 days. Bring to room temperature before serving for best texture.