These mini versions of classic cookies are soft-baked and delicious.
Preheat oven to 350 degrees. Whisk together flour, baking soda, and salt.
Beat butter and sugars with a mixer on medium-high speed until pale and fluffy, 3 to 5 minutes. Beat in egg and vanilla. Reduce speed to low. Beat in flour mixture in two additions, alternating with the sour cream. Stir in chocolate chips. Cover, and refrigerate dough until firm, about 1 hour.
Using a teaspoon, shape dough into 3/4-inch balls, and space 1 inch apart on parchment-lined baking sheets. Flatten slightly. Bake until pale golden brown and centers are set, 10 to 12 minutes. Let cool slightly on sheets on wire racks, then transfer to racks to cool completely. Cookies are best the day they are made, but they can be stored in airtight containers for up to 1 week.