To the bowl of a stand mixer fitted with the paddle attachment (or large bowl and electric mixer), add the butter, sugars, and beat on medium-high speed until creamed and well combined, about 3 to 4 minutes.

Stop, scrape down the sides of the bowl, and add the egg, vanilla extract, and beat on medium-high speed until well combined, about 2 minutes.

Stop, scrape down the sides of the bowl, and add the cream, and beat on medium-high speed until well combined, about 1 minute. The batter may look a little "grainy" and almost and if it's separated, this is okay.

Stop, scrape down the sides of the bowl, and add the flour, cornstarch, baking soda, salt, and beat on low speed until just combined, about 1 minute.

Stop, scrape down the sides of the bowl, and add the sprinkles, and beat on low speed until just combined, about 30 seconds.

Using a 2-tablespoon cookie scoop or your hands, form approximately 17 equal-sized mounds of dough. Place mounds on a large plate or tray, cover with plastic wrap, and refrigerate for at least 3 hours, up to 5 days. Do not bake with unchilled dough because cookies will bake thinner, flatter, and be more prone to spreading. After chilling, flatten each mound about half the original height.

Preheat oven to 350°F, line a baking sheet with parchment paper or spray with cooking spray. Place dough mounds on baking sheet, spaced at least 2 inches apart. Top each mounds with a generous pinch of sprinkles, pressing them down lightly so they adhere.

Bake for about 8 minutes or until edges have set and tops are just set, even if slightly undercooked and glossy in the center, don't overbake. Cookies firm up as they cool.

Allow cookies to cool on baking sheet completely.