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 until smooth.
Add in the flour mixture, mix until it is fully combined. Fold in the sprinkles and white chocolate chips. Evenly press the cookie dough into a greased square baking dish. Bake for 20-25 minutes.