Preheat the oven to 350F.
Grease a pan of your choice. (9x13, bundt pan, 2 dozen cupcakes, or if you want a layer cake, three 8- or 9- inch round pans.)
Cream butter and sugar together.
Add eggs and beat well.
Add 1 cup of the flour, followed by the baking soda, salt and cinnamon (and optional add-ins would go in here too).
Add remaining flour, beat well.
Add applesauce and you guessed it, beat well.
Pour and spread out in your desired baking pans.
You're going to have to play the baking time a little by ear here, as different pans and different ovens bake at different times. Luckily, it's so moist it's very forgiving, but you want to bake it until a knife inserted in the middle comes out clean. SEE NOTES FOR ESTIMATED BAKING TIMES.
Let it cool and ice with your desired glaze or frosting, I like a simple vanilla butter cream but sorry I don't have a recipe for it...I just wing it every time!