Crust: preheat oven 350 F. Line an 8x8 pan with parchment paper. Using a food processor, mix the crushed crackers and sugar. Mix in the cold butter and pulse to a coarse meal consistency. Press into the pan and 1 inch up the sides. Bake ~10 minutes.

Filling: trim the ends of the lemon and cut into thin strips and remove the seeds. Add the lemons to a food processor along with the yolks, butter, sugar, and vanilla. Blend until smooth. Pour into the baked crust, bake ~35 min. Cool completely and refrigerate.

Meringue: prepare 1 hour before serving. In a double boiler, warm the egg whites with the salt, sugar, and vanilla until the sugar has melted. Use a mixer to whip the egg whites to glossy, stiff peaks. Spread over the cooled bars and then broil until lightly browned. Store in the refrigerator.

Serving: dip a knife in hot water and cut the bars into 2 inch squares.