1Heat oven to 350°. Grease bottom and sides of rectangular pan, 13 x 9 x 2 inches, with shortening; lightly flour. Beat 1/2 cup butter and 3/4 cup brown sugar in small bowl with electric mixer on medium speed until fluffy. Beat in 1 cup flour on low speed. Press in pan. Bake 10 to 13 minutes or until light golden.
2Beat 1/4 cup butter and 1 cup brown sugar in large bowl on medium speed until fluffy. Beat in remaining ingredients except pecans and Marshmallow Frosting on low speed. Pour over crust. Sprinkle with pecans; press lightly.
3Bake 29 to 33 minutes or until set. Cool completely, about 1 hour. Frost with Marshmallow Frosting. For bars, cut into 8 rows by 4 rows, using hot, slightly damp knife. Store covered in refrigerator.
4Method for Marshmallow Frosting: Place corn syrup in small microwavable bowl. Microwave uncovered on High 1 to 2 minutes or until boiling. Stir in marshmallow creme. Beat egg whites, cream of tartar and cinnamon in medium bowl on high speed until soft peaks form. Beat in marshmallow mixture; continue beating on medium speed until stiff peaks form.