Preheat your oven to 350°F (175°C). Brush an 8-inch square baking dish with melted butter and line the bottom with parchment paper, leaving a 2-inch overhang on two sides.

In a food processor, grind graham crackers to a fine crumb. Add sugar and melted butter, then pulse until well blended and crumbly.

Press the crust evenly into the bottom of the prepared dish and about 1 inch up the sides.

Bake the crust until lightly browned, about 8–12 minutes. Let it cool for 30 minutes.

In a large bowl, whisk together egg yolks and sweetened condensed milk.

Add lemon juice and whisk until smooth.

Pour the filling over the cooled crust and spread it to the edges.

Bake until the filling is set, about 15 minutes.

Cool the squares in the pan on a wire rack, then refrigerate for at least 1 hour before serving.

Use the parchment overhang to lift the lemon squares from the pan, transfer them to a cutting board, and cut into 16 squares, wiping the knife between cuts for clean slices.