Add the 2 cups of frozen raspberries in a small saucepan over medium low heat. Allow to gently simmer with the lid off for 10 - 15 minutes to reduce the moisture and let them thicken. You know they are done when you scrape the bottom of the pan and the puree does not fall to the center.
In a large saucepan over medium heat, melt the ¼ cup butter and add 4 cups of marshmallows. Reduce heat to low and stir until marshmallows are melted and combined with butter into a smooth mix.
Add 5 cups of Rice Krispie cereal, cooled raspberry puree and ½ cup of mini marshmallows & gently fold cereal into melted marshmallow mixture. Be careful not to over mix and crush cereal. Before cereal is just combined, add ¾ cup of white chocolate chips, fold until they are just incorporated.
Transfer to a parchment paper lined baking dish and gently pat into place (avoid crushing). Prepare chocolate drizzle.
Melt chocolate chips and 2 tbsp of butter in a microwave or in a double boiler until smooth. Drizzle over krispie treats and store in the refrigerator for at least an hour before slicing and serving