Banana–Chocolate Chip Snack Cake with Salted Peanut Butter Frosting

Name: Banana–Chocolate Chip Snack Cake with Salted Peanut Butter Frosting
Ingredients: 6 tablespoons unsalted butter; 2 cups whole-wheat pastry flour (about 8 ounces); 3/4 teaspoon baking soda; 1/2 teaspoon kosher salt; 1 large egg; 3/4 cup mashed ripe banana (about 2 small bananas); 2/3 cup packed light brown sugar; 1/2 cup buttermilk; 1 teaspoon vanilla extract; 1/2 cup semisweet chocolate chips (about 3 3/8 ounces), plus more for garnish (optional); 3/4 cup creamy peanut butter; 2 tablespoons unsalted butter, softened; 1/2 teaspoon vanilla extract; 3/8 teaspoon kosher salt; 3/4 cup powdered sugar