COMBINE shortening, granulated sugar and brown sugar in large bowl; beat at medium speed until well blended. Add milk. Beat in eggs, one at a time. Add vanilla.
COMBINE flour, baking soda, cream of tartar and salt in separate large bowl. Mix into shortening mixture until well blended. Chill 1 hour.
HEAT oven to 350 degrees F.
ROLL out 1/3 of dough at a time to about 1/4-inch thickness on floured surface. Cut out with cookie cutters. Place 2 inches apart on ungreased baking sheets. Sprinkle with colored sugars and decors or leave plain and frost when cooled.
BAKE 6 to 8 minutes or until edges of cookies are slightly golden. Remove immediately to cooling rack.
Buttery Cream Frosting:
COMBINE powdered sugar, shortening and vanilla in bowl of electric mixer; slowly blend in milk to reach desired consistency.
BEAT on high speed for 5 minutes or until smooth and creamy. Tint frosting with food coloring, if desired.