Preheat oven to 350°F (175°C). Line an 8x8-inch (20x20 cm) pan with parchment leaving an overhang for easy removal.

In a bowl, stir together 150 g all-purpose flour, 50 g granulated sugar, 55 g light brown sugar, and ¼ tsp fine sea salt.

Pour in 113 g melted unsalted butter and ½ tsp vanilla extract. Mix until a cohesive dough forms.

Press the dough evenly into the prepared pan with the back of a spoon or an offset spatula.

Bake for 14–16 minutes, or until edges are lightly golden. Remove from oven and leave oven on.

In a large bowl, whisk 4 large eggs with 150 g granulated sugar until smooth.

Whisk in 40 g all-purpose flour until fully incorporated.

Stir in 160 g Meyer lemon juice and 1½ tbsp Meyer lemon zest. Strain the mixture through a fine sieve for an extra-smooth curd (optional).

Pour the lemon filling over the hot baked crust and return to the oven.

Bake for 18–22 minutes, until the filling is mostly set but still slightly jiggly in the center. An instant-read thermometer should read around 170–175°F (77–80°C) in the center.

Remove from oven and let cool on a rack for 30–60 minutes, then refrigerate for at least 2 hours to fully set.

Just before serving, sprinkle a thin, even layer of granulated sugar over the chilled bars (about 2–3 tablespoons across the surface).

Using a kitchen torch, move in a steady circular motion to melt and caramelize the sugar until it forms a golden-brown, crackling surface. If you don’t have a torch, place the pan under the oven broiler on high for 1–3 minutes—watch closely to avoid burning.

Let the sugar cool and harden, then lift the slab out of the pan using the parchment overhang. Slice with a sharp knife; warming the blade briefly between cuts gives cleaner edges.