• In a large mixing bowl, cream the butter and the sugar on high until there are no more lumps. Break apart any chunks of butter or sugar and scrape down the sides of the bowl with a rubber spatula.
• Add the vanilla extract and the sour cream and mix on a low setting until combined. Then add in the eggs and mix on low until just incorporated. Do not overmix as it will add too much air.
• Add in the baking soda, cornstarch, salt, and just one cup of the all purpose flour then mix again on low. Slowly add in the rest of the flour one cup at a time and continue mixing. After you add the last cup of flour, only mix until halfway incorporated with streaks of flour still in the batter. Then add in the nonpareil sprinkles and finish mixing by hand using a rubber spatula.
• Cover the bowl in plastic wrap and place in the refrigerator to chill for at least 30 minutes. The dough will be very sticky but will be firmer and easier to work with after chilling. Once the dough has chilled, preheat the oven to 375 F and line two baking sheets with parchment paper or a silicone mat.
• Use a medium 1 ½ tablespoon cookie scoop and drop each ball of dough about 4 inches apart. Lightly flatten them into thick discs with the bottom of a measuring cup or with your fingers. They will continue to spread and rise as they bake so make sure they have enough space between them.
• Place them in the oven to bake at 375 F for 8-10 minutes. Check at 8 minutes to see doneness. They should still be a little soft when they come out and have lightly golden bottoms. Allow them to cool in the pan for 3 minutes before transferring them onto a wire rack to cool completely.

For the frosting

• As it cools, prepare the frosting. In a microwave safe bowl, melt the premium baking chocolate by microwaving in 30 second increments on a defrost setting, stirring well each time until smooth. Set aside to cool for about 10 minutes. You don’t want it too warm that it will melt your butter.
• In a mixing bowl using a hand mixer, beat the butter until smooth and creamy. Then add in the slightly cooled and melted chocolate and mix on low until well combined.
• Gradually add the powdered sugar a little at a time and mix until fully incorporated. Add the heavy whipping cream, vanilla extract, and salt and whip until you have a smooth, spreadable frosting.
• Use a small icing spatula and frost 1 ½ tablespoons of frosting onto the cookies. Top with sprinkles and an animal circus cookie.