Prep your pan. Heat the oven to 350°F (175°C). Line an 8-inch square pan with parchment, leaving an overhang on two sides for easy lifting.

Make the crust. Crush the cookies into fine crumbs using a food processor or a zip-top bag and rolling pin. Stir the crumbs with the melted butter until the mixture looks like wet sand.

Press and pre-bake. Firmly press the crust into an even layer in the pan. Bake for 8–10 minutes until lightly golden at the edges. This sets the crust so it won’t go soggy.

Mix the filling. In a bowl, whisk the sweetened condensed milk, lemon juice, and lemon zest until smooth and slightly thickened. It will start to firm up as the acid hits the milk.

Pour and bake. Pour the filling over the warm crust and smooth the top. Bake for 12–15 minutes, just until the center barely jiggles when you nudge the pan. Don’t overbake.

Cool and chill. Let the pan cool at room temperature, then refrigerate for at least 2 hours. The chill helps the bars set for clean slices.

Slice and serve. Use the parchment to lift the slab out. Cut into 16 squares with a sharp knife, wiping the blade between cuts. Dust with powdered sugar if you like.