Preheat oven to 350 degrees. Mix together butter and sugars with electric mixer on medium speed until pale and fluffy, about 2 minutes. Reduce speed to low. Add salt, vanilla, and eggs; mix until well blended, about 1 minute. Mix in flour and baking soda. Stir in chocolate chips.
Spray mini-muffin tins thoroughly with non-stick cooking spray. Fill muffin cups with about 2 tbsp dough, slightly hollowing out the center. Bake cookies 7-9 minutes, or until lightly golden (do not overbake!)
Transfer cookies to wire racks. Let cool completely, then fill with frosting, using a pastry bag or sandwich bag with the corner tip cut off.