Preheat the oven to 350 degrees. Line an 8"x8" pan with foil and coat the foil with 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.
While the crust is baking, prepare the filling.
Beat the egg yolks with a 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.
Prior to serving, cut the bars into 9 equal pieces and prepare the whipped cream topping.
Place the heavy cream in a bowl and beat with a mixture until stiff peaks form. Fold in the sugar.
Place the whipped cream inside a piping bag fitted with a large star tip and pipe rosettes of whipped cream onto the bars.