anyone have a tried and true yummy recipe that can sit out? thanks.

How long will the cake "sit out"?

You can try pre-packaged banana pudding cups, tho you might want to mix it with some buttercream to make it less runny. These pudding cups require no refrigeration.

You can also try pureed baby food bananas, also mixed with buttercream to desired consistency.

There is a product called Fruit Fresh, an ascorbic acid powder, which is sprinkled onto sliced fruit (in this case bananas, or mixed into mashed bananas) to keep it from turning brown. Also could mix the "treated" bananas with buttercream.

You could add banana extract to any of the above to deepen the flavor

You could try an Italian Pastry Cream with Banana extract (instead of vanilla) and put sliced bananas in it (similar to what Sugarfrosted said).

Edited to add: The Italian Pastry Cream sets up really thick and makes an excellent filling for cakes.

thanks much.