I'm sure that anything tasty and beautiful will make a nice groom's cake, but here are a couple traditional recipes. Nothing noted about how the the baked one was decorated. However, I recall when I was given a piece of Groom's cake in a little box it had a very rich icing on top with almond paste under it.
From my file: (LOVE fruitcakes) These are designated Groom's cake. Unfortunately I didn't note exactly where I got the first one which is steamed and probably older than the second. (From something like NYT Ckbk, Gourmet, or perhaps Joy, Fannie Farmer, or Settlement). If it's important to anyone, I can explore and try to find the exact source. I think the use of fruit cakes at weddings is more traditional than the sort we use now. My fuzzy recollection is that even the whiter Bride's Cake used to have some fruit in it, too.
GROOM'S CAKE
2 sticks butter softened
2 1/4 cup confectioners' sugar
5 large eggs
1 1/2 cup all-purpose flour combined with 2 tsp cinnamon,
1 tsp ground allspice
1 tsp freshly grated nutmeg
1/2 tsp ground cloves
1/4 cup fresh lemon juice combined with 1/2 cup unsweetened bottled grape juice
1 Tbs grated lemon rind
1 1/2 cup raisins
1 1/2 cup finely chopped glaceed citron
1 1/2 cup coarsely chopped blanched almonds
1/3 cup sieved apricot jam
8" round straight sided baking dish with 3" deep sides lined with buttered wax paper.
In mixer cream butter til light and fluffy; add 2 cups confectioners' sugar, 1/4 cup at a time, beating and beat til smooth. Add eggs,1 x 1, beating after each addition. Add flour mixture and the juice mixture alternately a third at a time; stir in rind, fruits, almonds. Turn batter into dish; cover batter with a buttered round of wax paper; cover with double layer of foil secured with kitchen string. Set on rack in kettle with tight fitting lid; add enough simmering water to kettle to reach halfway up sides of dish; steam cake. Adjust heat as necessary to keep water at a simmer and adding more water as necessary for 2 1/2 hours to 3 hours or til cake tester inserted through foil into center of cake comes out clean.
Remove dish carefully from kettle, remove foil and wax paper. Let cake stand on rack 30 minutes. Run thin knife around inside edge of dish; invert rack over cake and invert cake onto it. Let cake cool completely. May be stored in airtight container for 1 week or frozen, wrapped tightly in plastic wrap for several weeks. Transfer to platter. Sift 1/4 cup confectioner's sugar over top and brush sides with apricot jam, heated. Yields 24 very thin slices.
GROOM'S CAKE (II) from the old Woman's Day Encyclopedia
4 cup sifted all purpose flour
1 tsp baking powder
1/2 tsp each of ground cloves, cinnamon, mace
2 cup butter
2 1/4 cup (1 #) firmly packed brown sugar
10 eggs, well beaten
1/2 lb each candied cherries and pineapple
1 lb dates, seeded and sliced
1 lb each seedless raisins and currants
1/2 lb citron, thinly sliced
1/4 lb each of candied orange and lemon peel
2 cup chopped nuts
1 cup each honey and molasses
1/2 cup cider
Sift flour, baking powder, spices together 3 times. Cream butter. Gradually add sugar; cream til light and fluffy. Add eggs, fruits, peels, nuts, honey, molasses, and cider. Gradually add sifted dry ingredients, beating after each addition til blended. Spoon into 3 loaf pans (10 x 5 x 3" each), greased, lined with heavy paper, and greased again. Bake in preheated very slow oven (250°f) for 3 1/2 to 4 hours. Makes 80 servings.
Half cake served at reception; remainder put in gift boxes & given to guests to take home.