In small bowl, combine milk, instant coffee and vanilla. In large bowl, beat shortening and butter with electric mixer on medium speed until light and fluffy. Gradually add sugar, one cup at a time, beating well on medium speed. When all sugar has been mixed in, icing will appear dry. Scrape sides and bottom of bowl often. Beat in milk mixture. Continue beat at high speed until light and fluffy.
Keep icing covered with a damp cloth until you are ready to decorate. For best results, keep icing bowl in refrigerator when not using. Re-whip before using.