Line two 9×9 inch pans with parchment paper, leaving an overhang, then set aside.
In a large pot, combine 8 cups mini marshmallows with butter. Melt over medium-low heat, stirring continuously, then remove from the heat and stir in the vanilla extract.
Stir in the Rice Krispies, then fold in the remaining 2 cups of mini marshmallows.
Divide the Rice Krispie treat mixture evenly between both prepared pans and gently press them into an even layer. Lightly spray your hands with cooking spray if needed to prevent sticking.
Let both pans cool at room temperature for 30 minutes.
Scoop a 1 inch layer of ice cream over one pan of treats and spread it into an even layer.
Lift the second block of treats out of the pan using the parchment paper, flip it over and place it on top of the treats with the ice cream layer.
Press down firmly and evenly, then peel off the parchment and freeze until solid, about 4-6 hours.
Use the parchment to lift the treats onto a cutting board, then cut into equal sized bars. If the treats are too hard, let sit at room temperature for 5–10 minutes.
Return any extras to the freezer to prevent melting.