Preheat oven to 375º

Cream butter and sugar. Add egg and vanilla and beat till smooth. Gradually add flour and stir until mixed.

Beat egg white with water until foamy.

Roll dough into small balls and place onto cooking sheets lined with parchment paper. Flatten. (I use a #100 cookie scoop and flatten with a small glass.)

Lightly brush tops of cookies with egg white. Decorate. (I use nonpareils.)

Bake for 7-10 minutes, on parchment paper lined cookie sheet (or ungreased cookie sheet) until dough is set and cookies are starting to brown along edges.

Remove to a rack to cool.