Preheat your oven to 350°F (175°C). Line a 9x9" baking pan with parchment paper.

In a food processor, pulse graham crackers until finely crushed. Melt butter and mix into the crumbs. Press mixture firmly into the bottom of the pan. Bake for 8-10 minutes until golden brown.

Zest and juice key limes. In a mixing bowl, combine key lime juice, zest, sweetened condensed milk, vanilla extract, and sour cream. Whisk until smooth.

Add egg yolks to the mixture and whisk until blended. Pour filling over cooled crust.

Bake for 15-20 minutes until center is slightly jiggly. Remove and let cool completely.

Cover with plastic wrap and refrigerate for at least 4 hours.

Whip heavy cream until stiff peaks form. Spread or pipe whipped cream over the bars.

Slice the chilled bars and serve garnished with lime zest.