In a medium bowl, whisk together flour, salt, and baking soda. In a large bowl, beat softened butter with granulated sugar until fluffy. Add in egg and vanilla extract, beat until smooth.
Add the dry ingredients in three additions, beating after each until all of the flour is incorporated. Fold in jelly beans. Cover and refrigerate for at least one 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.