Step 1: Preheat and Prepare the Pan

1. Preheat the oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper, leaving an overhang for easy removal.

Step 2: Make the Shortbread Crust

1. In a large bowl, combine shortbread cookie crumbs and melted butter. Mix until the crumbs are well coated. Press the mixture firmly into the bottom of the pan.
2. Bake for 10 minutes until golden, then let it cool slightly.

Step 3: Prepare the Lemon Filling

1. In a separate bowl, whisk together granulated sugar, salt, lemon juice, lemon zest, and eggs until smooth.
2. Pour the lemon mixture over the cooled crust.

Step 4: Bake the Lemon Layer

1. Bake for 20-25 minutes until the lemon layer is set and slightly firm to the touch. Let it cool completely before adding the meringue.

Step 5: Make the Meringue

1. In a heatproof bowl over a double boiler, whisk egg whites, sugar, and cream of tartar. Stir continuously until the sugar dissolves and the mixture reaches 160°F (71°C).
2. Remove from heat and beat with a mixer until glossy peaks form, about 5 minutes.

Step 6: Add the Meringue Topping

1. Spread or pipe the meringue over the cooled lemon layer. Use a kitchen torch or broil for 1-2 minutes to lightly toast the meringue until golden brown.

Step 7: Chill and Serve

1. Chill the bars for at least 30 minutes before slicing and serving. Use the parchment paper to lift the bars out of the pan for easy cutting.