In large bowl, cream shortening and butter with electric mixer. Add vanilla and lemon extracts. Gradually add sugar, one cup at a time, beating well on medium speed. Scrape sides and bottom of bowl often. When all sugar has been mixed in, icing will appear dry. Add lemon juice and beat at medium speed until light and fluffy. Add enough milk to thin frosting to desired consistency. Keep bowl covered with a damp cloth until ready to use.
*The lemon extract can be adjusted according to taste, however, I found more extract gave it a faker flavor. Use more lemon juice instead of milk if you want a stronger lemon flavor.