For cake: Preheat oven to 350?F. Butter and flour two 9-inch-diameter cake pans with 2-inch-high sides. Sift first 6 ingredients into medium bowl; set aside. Using electric mixer, beat butter and brown sugar in large bowl until light and fluffy. Add eggs 1 at a time, beating well after each addition. Beat in molasses. Beat in flour mixture alternately with stout in 3 additions each (mixture may look curdled). Beat just until smooth. Divide batter between prepared pans; smooth tops.
Bake cakes until tester inserted into center comes out clean, about 40 minutes. Cool cakes in pans on rack 10 minutes. Turn cakes out onto racks; cool completely. (Can be made 1 day ahead. Wrap in plastic; let stand at room temperature.
For frosting: Using electric mixer, beat cream and powdered sugar in large bowl until peaks form. Fold in minced crystallized ginger. Place 1 cake layer on platter. Spread 2 cups frosting over top. Top with second cake layer. Spread remaining frosting over top and sides of cake. Arrange orange slices, ginger slices and cranberries on top. (Can be made 2 hours ahead. Chill. Let stand at room temperature 20 minutes before serving.)