Mix the crushed graham crackers, melted butter, and a sprinkle of sugar. Press the mixture into a 9x13 pan.
Bake the graham cracker crust at 350°F for 8-10 minutes.
In a separate bowl, mix together the sweetened condensed milk, key lime juice, vanilla, sour cream or Greek yogurt, and egg yolks.
Pour the filling over the graham cracker crust.
Bake the bars at 325°F for 18-20 minutes.
Let the bars cool completely.
In a bowl, whip the heavy cream and powdered sugar until stiff peaks form.
Spread the whipped cream topping over the cooled bars and sprinkle with lime zest.
