Preheat oven to 350 F. Line a baking sheet with parchment paper or a silicone baking mat.
In a large mixing bowl, use a hand or stand mixer to beat the softened butter, sugar, and light brown sugar together until light and fluffy.
Mix in the vanilla extract, peanut butter, and egg.
Add the flour, baking soda, and cornstarch. Mix into the wet ingredients and combine.
Pour the sprinkles into a small bowl.
Form the dough into small balls, roll into your Valentine sprinkles bowl, and place onto the baking sheet.
Bake for 8 minutes or until lightly browned, and let cool for a few minutes before munching on them.
Serve Valentine's Day Peanut Butter Cookies, as a fun and sparkly dessert!