Preheat the oven to 350 degrees Fahrenheit. Lightly grease a 9-inch tart pan with a removable bottom and place it onto a baking sheet.

In a medium mixing bowl, combine the graham cracker crumbs, sugar, and melted butter. Stir until the mixture resembles wet sand and all crumbs are coated evenly.

Transfer the crumb mixture into the tart pan. Firmly press the crumbs into the bottom and sides using the bottom of a measuring cup or glass.

Bake the crust for 8 to 10 minutes or until lightly golden brown and fragrant. Remove from the oven and let cool slightly.

In a large bowl, whisk the egg yolks until smooth. Slowly add the sweetened condensed milk and whisk until creamy and fully combined.

Add the key lime juice and lime zest to the filling mixture. Continue whisking until smooth, creamy, and slightly thickened.

Pour the filling into the prepared crust and spread evenly with a spatula. Tap the tart pan gently on the counter to release air bubbles.

Bake the tart for 14 to 16 minutes or until the edges are set and the center still jiggles slightly.

Remove the tart from the oven and allow it to cool completely at room temperature for about 45 minutes.

Transfer the tart to the refrigerator and chill for at least 3 hours or overnight for the best texture.

Before serving, decorate the tart with whipped cream, lime slices, and extra lime zest.

Slice and serve chilled.