Preheat oven to 350°F and line your baking sheets with parchment paper.
In a large mixing bowl cream your butter, sugar and brown sugar until light and fluffy.
Add your vanilla extract, egg, and egg yolk in stir until well combined.
Add your flour, cornstarch, baking soda, and salt. Stir until just combined.
Using a cookie scoop, scoop your cookie dough into 1-2 inch balls and place on your baking sheet lined with parchment paper.
Roll each cookie in Valentines sprinkles. I used multiple different kinds and colors so use whatever kinds your hearts desires.
Bake in the oven at 350 F for 8-10 minutes.
Remove from oven, use a round glass or cookie cutter to scoot around the edges of the cookies to make them round and thicker. Top each cookie with a Hershey's kiss if you'd like.
Let cool. Serve, share & Enjoy!!