1. Prepare the Crust:

1. Preheat oven to 375°F (190°C). Line baking sheets with parchment paper.
2. In a large bowl, cream together the softened butter and sugar until light and fluffy. Beat in the egg and vanilla extract.
3. In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Mix in the sour cream until a soft dough forms.
4. On a lightly floured surface, roll the dough to 1/4-inch thickness. Cut into desired shapes with cookie cutters. Place cookies 1 inch apart on the prepared baking sheets.
5. Bake for 7-9 minutes, or until the edges are just barely starting to turn golden. The centers should remain soft. Let cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely. Decorate as desired.