Banana Split Sundae Cake

Name: Banana Split Sundae Cake
Ingredients: 1 stick (8 tablespoons) unsalted butter, plus more for the pan; 1 cup all-purpose flour; 1/4 teaspoon baking soda; 1/4 teaspoon fine sea salt; 1/2 cup mashed very ripe bananas (from 1 or 2 bananas); 1 large egg; 1/4 cup firmly-packed dark brown sugar; 1/2 cup granulated sugar; 1 teaspoon vanilla extract; 1/2 gallon (8 cups) vanilla ice cream, softened; 4 ounces semisweet chocolate, broken into large chunks; 3/4 cup heavy cream; 1/4 cup corn syrup; 3 tablespoons unsalted butter; 1/8 teaspoon kosher salt; 2 tablespoons unsalted butter; 3 ripe bananas, peeled, halved lengthwise and then halved crosswise; Sundae toppings: whipped cream, chopped salted peanuts, pretzels, dried banana chips, chocolate chips, peanut butter chips, toasted coconut flakes and maraschino cherries