Preheat the oven to 410°.
In the large bowl of your stand mixer, combine the cold cubed butter and both sugars. Fitted with the paddle attachment, mix ingredients on a medium speed for about 4 minutes or until creamy.
Add eggs, one at a time. Be sure to mix well after adding each one.
In a separate bowl combine flour, cornstarch, baking soda and salt. Whisk ingredients together and then add to the butter, sugar and egg mixture all at once. Mix until just combined. You do not want to over mix {this will heat up your butter}. Add your chocolate chips and sprinkles, mix by hand until evenly distributed.
Use a large cookie scoop {or about 3 tablespoons of dough} to scoop mounds of cookie dough onto a silicone mat {or parchment} lined baking sheet. Sprinkle the top of each cookie dough mound with a few additional heart sprinkles. Bake for 8-10 minutes or until the cookies are set and starting to turn golden brown.
Remove from the oven and allow the cookies to cool on the baking sheet for 5 minutes. Add an unwrapped chocolate heart to the middle of each cookie and allow the cookies to cool for an additional 3-4 minutes on the baking sheet. After that, move them to a cooling rack to cool completely and allow the chocolate hearts to set back up.
Store in an airtight container at room temperature for up to 4 days or freeze for up to 3 months.