Aunt Ettie'S Filled Sugar Cookies
["1 c. butter", "1 egg", "2 c. sugar", "3/4 c. sour milk (buttermilk best)", "1 tsp. soda, dissolved in sour milk", "1 tsp. vanilla", "flour to roll"]
["Chill dough before rolling.", "Roll 1/4-inch thick."]
["butter", "egg", "sugar", "sour milk", "soda", "vanilla", "flour"]