In a large pot, melt the butter on medium-high heat. Once the butter is melted add the pumpkin spice mallows. Reduce the heat to low, and mix with a silicone spatula until the marshmallows are just about melted. Then mix in the pumpkin pie spice.
Remove the pot from the heat and begin mixing in the 6 cups of rice krispies. Once half way incorporated into the melted marhsmallows mix in 1/4 cup of the pumpkin spiced white chocolate chips. Mix well then spray a 9x9 baking dish with cooking spray. Pack the rice krispies tightly into the pan using the spatula.
Cover the treats with plastic wrap and place in the refrigerator for at least 15 minutes.
Remove the treats from the fridge. Cut into 9 pieces (or cut the 9 in half to yield 18 pieces). Then, melt the remaining 1/4 cup of pumpkin spiced white chocolate chips in the microwave. Using a spoon drizzle the white chocolate on top of the pumpkin spice krispie treats. Place in the refrigerator for an additional 5 minutes so that the white chocolate can harden. Eat immediately or place in a sealed container for up to 2 days.