In a stand mixer, cream butter and sugar for about 1 minute, then add egg and vanilla. Stir in sour cream or plain yogurt. Combine salt, baking soda, and flour, then stir into dough just until combined.
Roll dough out on lightly floured surface to about ⅓-inch thick. Cut out cookies in desired shapes, then carefully slide a spatula under each cookie and place on cookie sheets about 2 inches apart.
Bake at 375F degrees for 7-8 minutes (they should be cooked through, but not browning on the edges yet). Allow to cool about 5 minutes, then transfer to a cooling rack. Cool completely, then frost with Buttercream Frosting (see below). If you’re adding sprinkles, put them on right after you frost each cookie.
Notes
BUTTERCREAM FROSTING: ¼ cup butter, softened 2 cups powdered sugar 1 tsp vanilla extract 2-3 T milk a few drops of food coloring (optional)
In a mixing bowl, cream butter. Beat in sugar and vanilla until crumbly. Gradually add milk until frosting reaches desired consistency. Add any desired food coloring.
Recipe by I Wish I Was a Muffin at https://iwishiwasamuffin.com/pillowy-soft-sugar-cookies/