In a medium bowl, whisk together flour, salt and baking soda. In a large bowl using either a hand or stand mixer, beat softened butter with granulated sugar until fluffy.
Add in eggs and vanilla extract, beat until smooth. Add in flour mixture in three seperate additions, beating after each until fully incorporated. Fold in m&ms and sprinkles. Cover and refrigerate for at least 1 hour.
Preheat oven to 350 F. Roll cookie dough into balls and place 2-inches apart onto ungreased baking sheets. Bake for 10-12 minutes.
