Adjust oven rack to middle position and preheat oven to 350˚ F.

Line the bottom and sides of an 8×8 inch pan with parchment paper. Allow the parchment to hang over the sides by about 2 inches for easy removal of the bars once chilled. Set aside.

Grind the vanilla wafer cookies in a food processor until mixture resembles fine crumbs.

Mix together finely ground vanilla wafer cookies, melted butter and brown sugar in a medium bowl. The texture should be similar to wet sand.

Transfer the cookie mixture into the pan. Using the flat part of a spatula, press the cookie crumbs evenly into the square pan.

Bake for 13 to 15 minutes. Remove the pan from the oven and set aside to cool for about 30 minutes.

Key Lime Pie Filling

In a large bowl, add the egg yolks and zest. Beat with a hand mixer on medium for 4-5 minutes, until the eggs lighten in color and thicken in texture.

Add the sweetened condensed milk and continue to beat on medium for another 3 minutes.

Whisk in the lime juice.

Pour the filling on top of the cooled cookie base. Place in the oven for 15-17 minutes until the filling is set but the filling will still wiggle as a whole when you gently shake the pan. Remove from the oven and let it cool on the counter for 30 minutes. Once cooled, place in the refrigerator for 3 hours or overnight.

Whipped Cream Topping

In a large bowl, use a hand mixer to beat the heavy whipping cream and sugar until firm peaks form.

Remove from the mixer and finish mixing by hand with a whisk. Do not over mix.

Spread the whipped cream on top of the key lime custard. Use an offset spatula to spread evenly. Chill for at least 30 minutes before slicing.

Once chilled, use the parchment overhang to remove the bars from pan. Use a sharp knife to slice into squares. For best results, clean the knife with warm water and dry with a clean towel between each slice.