• Preheat oven to 325°F and grease an 8-inch pie pan.
• In a medium bowl combine the graham cracker crumbs, sugar, and 4 tablespoons of the butter. Add more butter if needed.
• Using a fork, mix well. You want every crumb coated in the butter as this will be the glue that holds it together.
• Pour the graham cracker crumbs into the prepared 8-inch pie dish. Pat them flat with your hand and then use a kitchen glass to press flatter. Start at the center and work out to the sides. You can go as far up the sides as you would like.
• Bake the crust for 15 minutes.

KEY LIME PIE FILLING

• While the crust is baking, add the condensed milk, egg yolks, key lime juice, and zest to a medium bowl. Stir to combine.
• Pour mixture into the baked crust.
• Bake for 20-25 minutes. The pie is done when you see the tiny surface bubbles start to pop, or the internal temperature is 145°F.
• As soon as the pie comes to room temperature, chill in the refrigerator for at least 30 minutes.

WHIPPED TOPPING

• When the pie is almost done chilling, add heavy cream to a mixing bowl. Start mixing at the lowest speed, and then gradually increase speed to medium until the cream starts to get thicker. (The gradual progression prevents you from spraying yourself with cream.)
• When the cream starts to thicken, stop the mixer. Slowly add in the confectioners' sugar and then resume mixing again, starting with low speed and increasing to medium speed and eventually moving to a high speed.
• The cream will thicken and start to peak. Mix on high until the cream is thick and stiff. This happens quickly, the stage between soft and stiff peaks, so watch it closely.
• Top the pie with whipped topping and serve!