• Preheat the oven to 350°F. In a large bowl, use an electric mixer on medium-high speed to cream together ½ cup (1 stick) of softened unsalted butter, ½ cup of light brown sugar, and ¼ cup of granulated sugar for 2 minutes until the mixture is light and fluffy. Add 1 large egg, 1 teaspoon of vanilla extract, and 2 tablespoons of light corn syrup, mixing on low speed until everything is combined. Be sure to scrape down the sides of the bowl to incorporate all the ingredients.
• Next, add ¼ teaspoon of baking soda and ¼ teaspoon of salt, mixing for another 5-10 seconds until well combined. Finally, incorporate ½ cup of dark cocoa powder and 1 ¼ cups of all-purpose flour, mixing on medium speed until everything is thoroughly combined.
• Scoop the dough into ¼ cup (4 tablespoons) sized portions (I use a stainless steel cookie scoop!), roll them into balls, and gently flatten each ball into a ½-inch thick disc to encourage spreading rather than puffiness. Bake at 350°F for 11-12 minutes, being careful not to overbake. The centers may appear slightly wet but will continue to cook on the hot pan, allowing them to firm up without becoming overbaked. Allow the cookies to cool completely before decorating.

To Make Chocolate Ganache:

• In a medium-sized, heat-safe bowl (approximately cereal bowl size), place ¾ cup of semi-sweet chocolate chips. In a separate medium-sized bowl or large liquid measuring cup, heat ¼ cup of heavy cream in the microwave for 30-45 seconds, or until it starts to bubble (ensure your measuring cup or bowl is at least four times taller than the cream line, as it will expand and can overflow when heated). Alternatively, you can heat it on the stove, removing it once it begins to steam.
• Carefully use a hot pad to take the cream out of the microwave and pour it over the chocolate chips (do not stir yet!). Use a fork to press down the chips, ensuring they are fully covered by the cream. Let it sit for about 3 minutes, then stir with a fork; it may look thick and appear not to mix initially, but keep stirring until smooth and creamy. If the mixture doesn't fully melt, microwave it in 10-second increments at 50% power, stirring between each increment until smooth.

To Decorate:

• Spoon 1 tablespoon of chocolate ganache onto each cookie and top with rainbow chip sprinkles. Place the cookies in the refrigerator for 30-60 minutes to allow the ganache to harden. I recommend refrigerating the cookies, as they become even better and fudgier when chilled! However, if desired, you can keep them at room temperature for up to 2 days.