In a large saucepan, melt the butter over medium heat. Add the mini marshmallows and stir until melted and smooth.
Remove the pan from heat and stir in the vanilla extract.
Add the Rice Krispies cereal and granulated sugar to the marshmallow mixture, and gently fold until the cereal is fully coated with the melted marshmallow mixture.
Press the Rice Krispy mixture into the bottom of a 9-inch springform pan or a pie dish. Use a spatula or your hands (lightly greased) to press it down firmly to form an even crust. Allow it to cool and set while you prepare the cheesecake filling.
Prepare the Cheesecake Filling:
In a large mixing bowl, beat the softened cream cheese with an electric mixer until smooth and creamy, about 2-3 minutes.
In a separate bowl, whip the heavy whipping cream with the powdered sugar until soft peaks form.
Fold the whipped cream into the cream cheese mixture, adding the vanilla extract and sour cream (if using) for extra flavor. Mix until smooth and well-combined.
Taste the filling and adjust the sweetness if needed by adding more powdered sugar.
Assemble the Cheesecake:
Spoon the cheesecake filling onto the cooled Rice Krispy crust. Use a spatula to spread it evenly and smooth the top.
Refrigerate the cheesecake for at least 4 hours or until set. You can also refrigerate it overnight for the best results.
Serve:
Once the cheesecake has set, carefully remove the sides of the springform pan.
Top the cheesecake with fresh fruit, a fruit compote, or drizzle with caramel or chocolate sauce, if desired.
