Preheat the oven to 350 degrees. Combine the graham cracker crumbs, ¼ cup sugar, and melted butter. Mix until fully incorporated. Pat the crust evenly into each mini cupcake liner, fully lining the bottom and sides. Bake for 6 minutes. Let cool (about 20 minutes). Meanwhile, in a large bowl, beat together the egg yolks and ¼ cup sugar on high speed until thick. Add the condensed milk, lime zest, lime juice, and sour cream to the egg yolk mixture. Beat on medium speed until fully mixed. Spoon the mixture into the pie shells and freeze until frozen (about 2 hours). Beat the heavy cream in a large bowl until soft peaks form. Add the remaining ¼ cup sugar & vanilla and beat until stiff peaks form. Spoon the whipped cream on top of the mini pies). Return to the freezer and let sit until frozen (about another 2 hours). Decorate as desired.