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Prepare

Preheat the oven to 350°F (175°C). Line an 9x9-inch square baking pan with parchment paper, leaving an overhang on two sides to lift the finished bars out.

In a medium bowl, whisk together the flour, powdered sugar and salt until evenly combined.

Cut the cold unsalted butter into small cubes. Using a pastry cutter, two forks or your fingertips, work the butter into the dry ingredients until the mixture resembles coarse crumbs with some pea-sized pieces remaining. Stir in the vanilla extract until distributed.

Press the mixture evenly into the prepared pan, using the bottom of a measuring cup to compact and smooth the surface to an even layer about 1/2 inch thick.

Bake for 18–22 minutes, or until the edges are just turning golden and the center is set. Remove from oven and allow to cool slightly while you make the lemon curd. Do not remove from the pan.

In a medium heatproof bowl, whisk together the whole eggs, yolks and granulated sugar until smooth and slightly pale.

Whisk in the fresh lemon juice and lemon zest until fully combined.

Set a medium saucepan with 1–2 inches of water over medium heat to make a gentle simmer (double-boiler method). Place the bowl with the lemon mixture on top of the saucepan, making sure the bottom of the bowl does not touch the water.

Stir the mixture constantly with a heatproof spatula or whisk for 6–10 minutes as it warms. The curd will thicken gradually; you’re aiming for a temperature of about 170°F (77°C) or a custard-like consistency that coats the back of a spoon.

Remove the bowl from the heat. Immediately add the cold cubed butter a few pieces at a time, whisking until each addition is fully incorporated and the curd is smooth and glossy. Stir in the 1/8 tsp salt.

Pour the hot lemon curd evenly over the still-warm shortbread base, spreading to the edges. Return the pan to the oven and bake for 8–10 minutes more to set the filling. The curd should be slightly jiggly but mostly set.

Remove from oven and allow to cool to room temperature on a wire rack for at least 1 hour. For best slices, chill for 2 hours or up to overnight.

If chilled, remove the lemon bars from the refrigerator about 15–20 minutes before topping so they come slightly closer to room temperature.

Preheat your oven to 325°F (160°C) if you plan to bake the meringue briefly to set it; alternatively use a kitchen blowtorch for a browned finish without re-baking.

In a very clean, dry bowl, combine the egg whites and cream of tartar. Using an electric mixer on medium speed, whip until soft foamy peaks form.

Gradually add the 3/4 cup granulated sugar, about 1 tablespoon at a time, while continuing to beat. Increase speed to high and whip until glossy stiff peaks form and the sugar is fully dissolved (rub a little between your fingers to check for grittiness). Add the 1/2 tsp vanilla and whip briefly to incorporate.

Using a spatula or piping bag, spread or pipe the meringue over the chilled lemon layer in an even layer or decorative peaks, making sure to seal the meringue to the edges to prevent weeping.

To set and lightly brown the meringue: Option A (oven): Bake at 325°F (160°C) for 6–8 minutes until the tops are pale gold. Option B (torch): Use a kitchen torch to carefully brown the peaks until evenly toasted. Allow the meringue to cool for 10–15 minutes.

Optional: Sprinkle the very top with the 1/2 tsp finely grated lemon zest for a fresh aromatic finish.

Use the parchment overhang to lift the bars from the pan. Slice into 16 squares with a sharp knife, wiping the blade between cuts for clean edges. Serve chilled or at cool room temperature.