Banana Cake with PenucheFrosting

"The correct name of this frosting as it has been known in my family for at least 4 generations is panocha frosting. Panocha is a spelling variant of penuche that was once popular in Hawaii, and was localized from penuche to panocha. Panocha is also a type of cane sugar and a type of fudge-like candy. I think of this as my grandmother's recipe, but it's actually her mother's or her mother-in-law's...either way, it was a special cake that she would make for my father's birthday, as it's his favorite cake (and mine too). It's a simple seeming cake (no vanilla?! not a spice to be found?!), but it's like your favorite banana bread, only lighter and fluffier, and the frosting truly makes this cake. If you're into presentation, you'll want to follow my grandmother's lead and double this recipe, a four-layer cake is much more impressive. I never add the nuts, and I've had no problem substituting all-purpose flour. I've even been lazy and not separated the eggs, and it has turned out just fine, albeit with a bit denser crumb...."