Preheat oven to 350 degrees. In a large mixing bowl, beat the butter and cream cheese.
Add both sugars and beat well. Then add the egg and vanilla and blend well. In a small bowl, mix together the flour, cornstarch, baking soda, and salt. Add this mixture to the butter mixture and mix well. Stir in the chocolate chips and all the jimmies/sprinkles.
Roll into balls about 1 ½ inches round and place onto a baking sheet. Dip a glass into a little sugar and press each cookie down a little.
Sprinkle on the blue sugar. Bake for 8-10 minutes and remove and cool cookies. Melt the blue chocolate per package directions and drizzle a little over each cookie and let it dry.