Preheat the oven to 350 F. Line a 12 cup muffin pan with paper liners. In a medium bowl, whisk together flour, salt, and baking soda. In a large bowl, mix together butter, peanut butter, and both sugars until fluffy.
Add in the egg and vanilla extract, and mix until smooth. Fold in the sprinkles. Evenly divide the cookie dough between the paper liners. Bake for 12-15 minutes.