Preheat the oven to 350 F. In a medium bowl, whisk together flour, salt, and baking soda. In a large bowl, combine butter with sugar until fluffy. Add in egg and vanilla extract, and mix until smooth.
Add in the flour mixture, and mix until it is fully combined. Fold in the sprinkles. Place the powdered sugar into a shallow dish. Roll the cookie dough into balls, and roll each one into the powdered sugar.
Place the cookies onto a large ungreased baking sheet. Bake for 10-12 minutes.