Preheat oven to 350°F. Line a 9x9” pan with foil and spray with cooking spray. (The foil is necessary for these bars! You can use parchment if you prefer.)
Make the crust by stirring together the cookie crumbs and melted butter. Press into the bottom of your pan. Bake for 14 minutes.
While the crust is baking, make the filling. Whisk sugar, salt, lemon juice, and zest in a medium bowl. Whisk in eggs. Once crust is done, whisk the mixture again, then carefully pour it evenly over the crust. Bake an additional 20 minutes or so, until the edges start to brown and the top looks solid.
Cool completely on the counter, then cover and chill until cold. It will be chilled in about 2-3 hours, but you can make the bars up to 2 days ahead and store them in the refrigerator.
When ready to serve (or within a few hours of serving), make the meringue. Remove the lemon pie bars from the refrigerator while you make the meringue.
Fill a saucepan with about 2-3 inches of water. Bring to a boil. Find a bowl that will fit on top of the pan without touching the water. (I like to use a glass bowl over a 2 Qt. saucepan.)
Whisk the egg whites and the sugar in the bowl. Place it on top of the pan that’s over the boiling water (over medium-high heat). Whisk constantly for about 5-7 minutes, until the mixture reaches about 140°F. You can use a candy thermometer if you have one, or even a (clean) meat thermometer to measure the temperature.
Immediately transfer the mixture to a stand mixer fitted with a whisk attachment. Beat at high speed for until stiff peaks form, about five minutes depending on your mixer. Your meringue is now ready! (You can also use a hand mixer but it will take a lot longer.)
Use the foil to remove the lemon bars from the pan. Remove foil and place on a cookie sheet or serving plate (depending on how you’re toasting the meringue.) Frost the top with meringue. Really heap it on there!
Use a kitchen blowtorch to lightly brown the tops of the meringue. Or, you can place the pie under the broiler for just minute or two - do NOT walk away from the stove!
Slice and serve within a few hours.