In a large bowl or stand mixer cream together the butter and sugar until well combined. Beat in the egg and vanilla extract.
In another bowl, combine the dry ingredients: flour, baking powder and soda.
Slowly add in the dry ingredients to the mixer. You may want to stir by hand as the dough will get thick. Add 1 tbsp of buttermilk at a time to moisten the dough without making it too sticky.
*Preheat oven to 350 degrees. If rolling out for cutouts, chill dough for about 1 hour before preheating oven. Can be made into round sugar cookies right away too.
Flour a flat working surface generously. If dough seems too sticky, add flour to hands for working with dough, and divide in the bowl into about 3 sections for rolling. Using 1/3 of the dough, flatten and roll out with a rolling pin, continue to add flour while you work with it to avoid sticking.
Roll to desired thickness, create cutouts using your favorite cookie cutters. Arrange on baking sheet leaving about 2 inches between each cookie as they will spread during baking.
Bake at 350 degrees for about 8-11 minutes depending on cutout thickness. If you like a crunchier cookie leave in longer, and less time for a softer cookie.
Cool on a cooling rack. Decorate with your favorite icing and sprinkles.
For royal icing recipe see the link in the original post. This worked great and left a smooth finish that dries for clean cookie storage.
I put the icing in a shallow bowl and dipped the top, scraped excess for a smooth surface for decorating.
I used an assortment of colored small tip icing gels and some various sprinkles. Have fun!