Combine flour and milk in a small saucepan; cook over low heat, stirring constantly with a wire whisk, 3 minutes or until mixture resembles a soft frosting and is thick enough to hold its shape. (Do not boil.) Remove from heat; let cool.
Beat shortening and butter at medium speed of an electric mixer until creamy; add flour mixture, orange extract, and salt, beating well. Gradually add sugar, beating at high speed 4 to 5 minutes or until fluffy.