Place graham crackers in a ziploc bag and roll with rolling pin to crush. Mix with butter and set aside.
Cream mascarpone cheese in mixer until smooth, then add sweetened condensed milk and mix again until smooth. Then add key lime juice and mix until smooth.
Defrost the whipped topping and fold it into the cheese mixture.
Fill silicone cupcake pan about 3/4 of the way full and top with the graham cracker crumbs.
Place in the freezer for 4 hours or overnight.
When ready to serve, unmold pies upside down by carefully squeezing each one gently. Place in mini dessert cups if desired.
Use piping bag to garnish with whipped topping and a key lime slice.