Preheat the oven to 350°F and line a square baking pan with parchment paper.

In a bowl, mix graham cracker crumbs, sugar, and melted butter until fully combined.

Press the mixture firmly into the pan to form an even crust. Bake for 8 to 10 minutes, then let it cool completely.

In a large bowl, beat softened cream cheese until smooth and lump-free.

Add sugar and mix until fully combined, scraping down the bowl as needed.

Add eggs one at a time, mixing slowly after each addition just until incorporated.

Add sour cream, key lime juice, lime zest, and vanilla extract. Mix gently until smooth.

Pour the filling over the cooled crust and spread evenly with a spatula.

Tap the pan lightly to remove air bubbles.

Bake for 30 to 35 minutes until the edges are set and the center is slightly jiggly.

Turn off the oven and let the bars rest inside briefly with the door slightly open.

Remove and cool completely at room temperature.

Refrigerate for at least 3 hours until fully set.

Lift from the pan, slice into bars, and serve.