Make the Crust

1. Preheat the oven to 325°F.
2. Spray a 12-cavity mini cheesecake pan or muffin tin with good-quality baking spray.
3. In the bowl of a food processor, pulse graham crackers to fine crumbs. Transfer to a medium mixing bowl, add the melted butter and sugar, and mix until well combined.
4. Distribute the mixture evenly in the mini cheesecake pan; press the mixture down firmly into an even layer in each cavity. 
5. Bake until lightly brown (5 minutes). Remove from the oven and set aside to cool.

Make the Cheesecake Filling

1. In the bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese until smooth. Add the sour cream and granulated sugar and mix until well combined. Add the key lime juice, zest, vanilla extract, and green food dye and mix until fully combined, scraping down the sides of the bowl as needed. Add the egg and mix on low speed until just combined.
2. Distribute evenly among the cavities of the cheesecake pan.
3. Bake at 325°F until the tops of the cheesecakes are set (15– 18 minutes).
4. Remove from the oven and cool to room temperature (at least 1 hour). Cover tightly with plastic wrap and refrigerate for at least 3-4 hours or overnight. 
5. Remove the cheesecakes from the pan once thoroughly chilled.
6. Garnish with whipped cream if desired.