Eggnog Thumbprints

In a large bowl beat butter until softened. Add sugars and beat until fluffy. Add egg, vanilla, salt and beat well. Add flour and mix until well combined. Cover dough and chill for about 1 hour. Shape dough into 1" balls and place 2" apart on an ungreased cookie sheet. Press centers down slightly with thumb. Bake at 350? for 12 minutes or until just starting to turn golden. Cool. When cookies are cool, make Eggnog filling: Beat butter in small bowl until softened. Add powdered sugar and beat until fluffy. Add rum and beat well. Spoon about ? tsp filling into the center of each cookie. Sprinkle filled cookies with nutmeg. Chill until filling is firm. Make approximately 2 dozen.