Preheat oven to 350°F (177°C). Line two 12-count muffin pans with muffin liners. Set aside. In a large bowl using a handheld mixer or stand mixer with paddle attachment, cream the butter and sugars together on medium speed until fluffy and light in color. Mix in egg and vanilla. Scrape down the sides as needed. In a separate bowl, combine flour, cornstarch, baking soda and salt. On low speed, slowly mix into the wet ingredients. Stir in chocolate chips. Dough will be thick. Press 1.5 Tablespoons of dough into each muffin liner. Bake for only 10 minutes. They will not be cooked through at this point, but they will be going back in the oven. With a handheld mixer on medium speed, beat the cream cheese, sugar, egg, and vanilla together until completely smooth. Stir in the sprinkles, making sure not to overmix so their color does not bleed. Dollop 1 heaping Tablespoon of cheesecake batter onto each cookie cup, spreading it to make sure it completely covers the cookie. Return the cookie cups to the oven and continue to bake for about 18 more minutes, making sure the tops of the cheesecake does not get too brown. The cups are done in the oven when the cheesecake topping no longer jiggles when you shake the pan. Cover the cups with aluminum foil if the tops are getting too brown too soon. Allow to cool and enjoy. Makes 24 cups. Cookie cups stay fresh covered at room temperature for 12-24 hours, and then must be refrigerated after that for up to 4 more days.