Preheat the oven to 350°F. Line an 8x8-inch baking pan with parchment paper or foil, leaving an overhang on the sides. Lightly coat with cooking spray and set aside.

In a medium bowl, combine the graham cracker crumbs, granulated sugar, and melted butter. Mix until the crumbs are evenly moistened.

Press the graham cracker mixture firmly and evenly into the bottom of the prepared baking pan.

Bake the crust for 10 minutes. Remove from the oven and set aside to cool slightly.

Lower the oven temperature to 300°F.

In a large mixing bowl, beat the softened cream cheese with an electric mixer on medium speed until smooth.

Scrape the bottom and sides of the bowl. Add the egg yolks and beat until fully incorporated and smooth.

With the mixer on low speed, add the sweetened condensed milk, key lime juice, and lime zest. Mix until fully combined.

Pour the key lime filling over the prepared graham cracker crust. Spread into an even layer.

Bake for 35 to 40 minutes, or until the filling is set but still slightly jiggly in the center.

Remove the pan from the oven and allow the bars to cool at room temperature for 30 minutes.

Transfer the pan to the refrigerator and chill for at least 2 to 3 hours, or until fully set.

In a large bowl, beat the cold heavy cream and powdered sugar on low speed until thickened. Increase the speed to medium-high and whip until stiff peaks form.

Spread the whipped cream evenly over the chilled key lime bars. Refrigerate for an additional 30 minutes.

Use the parchment or foil overhang to carefully lift the bars from the pan. Cut into squares with a sharp knife. Garnish with lime zest before serving.