In a large pot, melt the butter. Then stir in the pumpkin, maple syrup, spices, and vanilla.
Reserve 1 cup of the mini marshmallows and add the rest to the pot. Heat on medium heat, while stirring, until melted and smooth.
Add the rice crisp cereal and stir to combine, then stir in remaining marshmallows.
Coat a 9x13 pan with butter or cooking spray, then press the cereal mixture into the pan and place in the refrigerator for 30 minutes to set.
Turn out to a cutting board and cut into squares
In a microwave or double boiler, melt the white chocolate until smooth. Dip each square in the chocolate and then decorate as you desire.
Alternatively, you could drizzle the chocolate instead of dipping.