Preheat oven to 300°F. Grease and flour (or use Baking Pam) a large (12 cup) Bundt pan or two loaf pans. Set aside.
In a large mixing bowl, cream the butter, margarine, and cream cheese until smooth.
Add the sugar and beat until very light and fluffy.
Alternate adding eggs and flour. Beat only until the yolks disappear and all flour is incorporated. Do not over-beat.
Bake at 300°F for 1 hour 45 minutes.
Allow the cake to cool 30 minutes before removing from the pan.
Notes
This recipe has also been tested multiple times using all butter (unsalted only) instead of the margarine and butter combo. The cake bakes more quickly when made with just butter and is a little darker around the edges. IMPORTANT: If using all butter instead of margarine, reduce the baking time to 90 minutes.
If you don't have jumbo eggs, use 7 large eggs.
My mother-in-law never added salt or flavorings but I've been adding 1 tablespoon vanilla to the recipe as well as 1/2 teaspoon salt, if using unsalted butter.
Nutrition information is calculated using an ingredient database and should be considered an estimate. When multiple ingredient alternatives are given, the first listed is calculated for nutrition. Garnishes and optional ingredients are not included.