Key Lime Pie Filling
1-Use a hand mixer with the whisk: Use a hand mixer with the whisk attachment to whip the heavy whipping cream with the sugar until stiff peaks form. Set aside.
2-Use a hand mixer with the beater: Use a hand mixer with the beater attachments to whip the softened cream cheese until smooth. Then, add the sweetened condensed milk and mix until smooth. Slowly add lime juice, mixing after each addition. Mix until smooth. Note: If using a different brand of lime juice (or fresh limes) I suggest taste-testing the mixture a few times as you add the lime juice to ensure the flavor is just right. Fresh limes tend to be bolder and brighter than store-bought juice.
3-Use a spatula to gently fold in: Use a spatula to gently fold in the lime zest to taste. Add as much as you like; you may not want the full amount. Fold in about 3/4 cup of the whipped cream (reserving the rest for topping the jars) until the mixture is smooth. Chill for 6 hours (longer or even overnight is fine).

Crust Layer
4-After mixture has chilled, prepare the crust: After mixture has chilled, prepare the crust. In a small bowl, mix the graham cracker crumbs, sugar, and melted butter together thoroughly. Divide mixture evenly among eight 4-oz mason jars and gently wiggle each jar to even out the crust. Avoid packing it down as it makes it hard to eat later.
5-Scoop the filling evenly into the crust-lined: Scoop the filling evenly into the crust-lined jars, about 1/3 cup of filling per jar. Fill a piping bag with the remaining whipped cream (use a large star tip) and pipe a star or rosette on top of each jar. Sprinkle with additional lime zest if desired.