Preheat the oven to 350 degrees Fahrenheit. Line an 8x8 pan with parchment paper and coat with non-stick cooking spray.
Place the graham cracker crumbs, sugar, and butter in a bowl and mix until well combined.
Firmly press the graham cracker mixture into an even layer in the bottom of the pan.
Bake the crust for 10 minutes.
Key Lime Filling
Beat the egg yolks with an electric hand mixer until smooth and creamy, 2-3 minutes. Slowly pour in the condensed milk, continuing to beat the mixture.
Add the lime juice, lime zest and sugar, then beat until completely smooth.
Pour the filling over the crust.
Bake for 15 minutes or until filling is just set.
Cool the bars completely then refrigerate for at least 4 hours or up to 3 days.
Whipped Cream
Place the heavy cream in a bowl and beat with a mixture until stiff peaks form. Fold in the sugar.
Before serving, spread the whipped cream on top of the chilled bars.
Cut the bars into 9 equal pieces and garnish with lime zest and wedges.