Preheat the oven to 350 F. In a medium bowl, whisk together flour, baking soda, and salt. In a large bowl, combine softened butter with sugar until fluffy.
Add in egg and peppermint extract, mix until smooth. Gradually add in the flour mixture, mixing until a thick dough forms. Fold in sprinkles.
Roll the cookie dough into balls, and place at least 2-inches apart onto ungreased baking sheets. Bake for 10-12 minutes.