Sift together baking soda, salt, baking powder, and flour. Set aside.

In a large mixing bowl, cream together butter and sugar. Beat for about 3 minutes.

Add eggs and vanilla. Beat for another 3 minutes.

Add flour alternately with sour cream in three additions. Begin and end with flour.

Cover dough with plastic wrap and refrigerate overnight or 8 hours.

Preheat oven to 375℉. Remove chilled dough from the refrigerator. Divide dough in half. Place dough on a lightly floured surface.

Roll out dough 1/4-inch thick. Brush off any remaining flour.

Cut out dough with a lightly floured cookie cutter. Carefully place cut cookies on a parchment-lined baking sheet.

Bake in preheated oven for 8-10 minutes or until the edges are barely beginning to turn golden. Remove from oven and allow cookies to cool 5-10 minutes on baking sheet. Transfer to cooling rack.

In a large mixing bowl, add cream cheese and butter. Beat until smooth and creamy.

Mix in powdered sugar and vanilla. Mix until smooth and well blended.

Ice cookies with a thin metal spatula or spoon icing into a bag fitted with a star tip and pipe icing onto the tops of the cookies. Add sprinkles, drageés, or sparkling sugars, if desired.