Preheat your oven to 350°F (175°C). Line a 9x9-inch baking pan with parchment paper for easy removal.

In a food processor, pulse about 1 ½ cups of graham crackers until finely crushed. Add ½ cup of melted butter and mix until the texture resembles wet sand. Press this mixture firmly into the bottom of the prepared pan to form an even crust.

Zest and juice about 4-6 key limes. In a mixing bowl, combine the key lime juice, zest, one can of sweetened condensed milk, 1 teaspoon of vanilla extract, and ½ cup of sour cream. Whisk until smooth and creamy.

Gently stir in 4 egg yolks into your creamy filling. Taste the mixture and adjust sweetness if needed before pouring it over the cooled crust.

Carefully pour the filling over the crust in the pan and spread it evenly. Bake for 15-20 minutes, or until the bars are set but slightly jiggly in the center.

Once out of the oven, allow the Lime Pie Bars to cool at room temperature for about 30 minutes. After cooling, transfer the pan to the refrigerator and chill for at least 2 hours.

In a separate bowl, whip 1 cup of heavy cream until stiff peaks form.

Spread the whipped cream evenly over the chilled bars and carefully slice into squares or rectangles.