Preheat the oven to 350 F. In a medium bowl, whisk flour, salt, and baking soda together. In a large bowl, mix butter with peanut butter and both sugars until fluffy. Add in the egg and vanilla extract and mix until smooth.
Add in the flour mixture, and mix until fully combined. Fold in the M&Ms, white chocolate chips, and sprinkles. Roll the cookie dough into balls and place onto a large ungreased baking sheet at least 2-inches apart. Bake for 10-12 minutes.