We suspect that "great" refers to the cholesterol level rather than to the taste, but, courtesy of the nice ladies who hosted Mount Vernon's Christmas tour (which really was great, complete with period costumes, a camel named Aladdin, and plenty of lusty "Hear ye, hear ye"s):
"Take 40 eggs divide the whites from the yolks & beat them to a froth then work 4 pounds of butter to a cream & put the whites of the eggs to it a Spoon full at a time till it is well work'd then put 4 pounds of sugar finely powdered to it in the same manners then put it in the Youlks of eggs & 5 pounds of flower & 5 pounds of fruit. 2 hours will bake it add to it half an ounce of mace & nutmeg half a pint of wine and some frensh brandy."
The transcriber of Martha's recipe may have sipped a bit too much frensh brandy before she sat down to work.
Cakes like this typically were served on Twelfth Night (January 6, the last day of Christmas, and George and Martha Washington's wedding anniversary. Here's the same recipe adapted for the 21st century, also courtesy of Mount Vernon:
1 pound butter
1 pound sugar
1 1/4 pounds flour
1 1/4 ounces assorted fruit and nuts*
2 1/2 t. ground mace
2 1/2 t. ground nutmeg
2 ounces wine
2 ounces French brandy
1. Preheat oven to 350 degrees.
2. Separate eggs whites from yolks, and set yolks aside. Beat the whites to a soft peak.
3. Cream the butter. Slowly add the beaten egg whites, one spoonful at a time, to the butter.
4. Slowly add the sugar, one spoonful at a time, to the egg whites and butter.
5. Add egg yolks.
6. Add flour slowly.
7. Add fruit.
8. Add mace, nutmeg, wine, and brandy.
9. Lightly grease and flour a 10-inch springfrom cake pan. Pour batter into pan and bake about 75 minutes. Let cool before icing.
* The following items are suggested based on what would have been available to Mrs. Washington, either fresh or dried. Nuts would have been considered fruit:
5 ounces pear, peeled, cored, and diced
9 1/2 ounces apple, peeled, cored, and diced
3 1/2 ounces raisins
2 ounces sliced almonds
Adaptation of an 18-Century Icing
1. Beat three egg whites and two tablespoons powdered sugar. Repeat additions of sugar until you have used one and a half cups of sugar.
2. Add one teaspoon grated lemon peel and two tablespoons orange-flower water. Beat until the icing is stiff enough to stay parted when a knife cuts through it.
3. Smooth it onto the cake.
4 Let it dry and harden in a 200-degree oven for one hour. (Note: Icing will be brittle when cut with a knife.)