Step 1

Preheat oven to 350°F. Melt butter and set aside. Finely crush graham crackers in food processor, blender or freezer baggie with rolling pin until all the same size. Add in sugar and pulse a few times until blended, pour in butter and stir with fork or pulse a couple times until mixed. Reserve 1/4 cup crumb mixture for topping, if desired.

Step 2

Pour crust mixture into 9" deep dish pie dish and using hands, press into bottom and up sides, evenly. Bake for 6-8 minutes, just golden, not browned. Remove from oven and cool completely on wire rack.

Step 3

*If needed, cool for 10 minutes on rack, then transfer to freezer for 20-30 minutes to cool completely.

Step 4

Preheat oven to 350°F.

Step 5

Wash, dry and zest limes, set zest aside until ready to use. Squeeze 3/4 cup of lime juice (about 24 key limes, or 6 Persian limes). Pour lime juice, sweetened condensed milk, sour cream, egg yolks (if using) and zest into the bowl of a stand mixer and mix on low until combined, then increase to medium-high for 2-3 minutes. Scraping down sides once or twice. DO NOT SKIP THE LONGER WHIPPING.

Step 6

Whip until batter is thickened.

Step 7

Pour Key Lime filling into COOLED graham cracker crust. Bake at 350 for 15-20 minutes until center is set, but still jiggles slightly when shaken. DO NOT ALLOW TO BROWN. Remove from oven to cooling rack and cool for 30 minutes. Place in fridge for at least 3 hours -- if you remove sooner it will still taste good, it will just not be quite as set if you had let it sit longer in the fridge. See notes for details if making key lime mini pies.

Step 8

While your pie is cooling, make whipped cream.Pour cold whipping cream into cool bowl and whip until stiff peaks form. Add vanilla and powdered sugar, mixing on low until combined, then increase to speed to medium-high and whip until thick, almost to a light butter stage.

Step 9

Scoop out and into piping bag with star tip. Whipped cream in bag may be kept in fridge until ready to garnish pie. Garnish with whipping cream stars, a little lime zest, graham cracker crumbs and a slice of lime. Keep refrigerated until ready to serve and chill all leftovers.