While the crust is baking, whisk together sugar, salt, and lemon zest. Add lemon juice and eggs, whisking until smooth and fully combined.
Pour the filling over the warm crust.
Bake for 18–22 minutes, until the edges are set and the center still has a slight wobble.
Allow to cool completely, then refrigerate for at least 3 hours or overnight until firm.
Meringue Topping
Fill a saucepan with about 2 inches of water and bring to a gentle simmer.
In a heatproof bowl set over the saucepan (without touching the water), whisk egg whites and sugar continuously for 5–7 minutes, until the mixture reaches 140°F (60°C) and the sugar dissolves.
Transfer to a stand mixer and beat for 5–7 minutes, until thick, glossy, and holding stiff peaks.
Assembly
Lift the chilled bars from the pan using the foil overhang.
Spread the meringue evenly over the lemon layer, creating decorative swirls.
Toast the top with a kitchen torch or briefly under a broiler for 1–2 minutes, watching closely to prevent burning.
Slice into squares using a hot, clean knife for sharp edges.
