2 1/2 cups (about half a 10oz package) of mini marshmallows
4 cups crispy rice cereal
1 1/2 cups heavy cream
1 envelope unflavored gelatin
2/3 cup granulated sugar
2 packages of cream cheese, cut into small chunks and softened 30 minutes at room temperature
2 tablespoons lemon juice
1 teaspoon vanilla extract
Line a 9 X 13 rimmed baking pan with aluminum foil. Spray inside with non-stick spray and set aside.
In a large pot, melt butter over medium low heat. Add in marshmallows and stir until melted, then remove from heat. Pour in the crispy rice cereal and stir until thoroughly combined. Empty into the lined baking pan and press flat with the back of a spoon. Set aside to cool.
Pour 1/4 cup heavy cream into microwave-safe measuring cup. Add gelatin and stir with a fork to combine. Let stand about 5 minutes then microwave for about 30 seconds, or until cream is bubbling and gelatin is completely dissolved.
Beat remaining 1 1/4 cups heavy cream and sugar in a stand mixer (or hand held) until soft peaks form. Add softened cream cheese and beat at medium-low speed about 3 minutes (a few chunks will remain). Add lemon juice, vanilla, and salt and continue to beat at medium speed until combined, about 2 more minutes. Scrape bottom and sides of bowl. Increase speed to medium-high and beat until mixture is smooth, about 3-6 minutes. Add dissolved gelatin mixture and continue to beat at medium-high until smooth and airy, about 2 minutes.
Pour cheesecake layer onto crispy rice layer and smooth the top and edges.
Cover the pan loosely with plastic wrap and refrigerate for 2 hours. Cut into squares and top with whipped cream or fresh fruit or sprinkles.