Double Banana Cake

Name: Double Banana Cake
Ingredients: 1 1/2 cups (3 sticks) unsalted butter plus more for pans, room temperature; 3 3/4 cups all-purpose flour; 1 1/2 teaspoons baking soda; 1 1/4 teaspoons kosher salt; 2 1/4 cups sugar; 6 large eggs; 3 cups coarsely mashed very ripe bananas (about 6 large); 3 /4 cup sour cream; 1 cup (2 sticks) unsalted butter, room temperature; 4 cups powdered sugar; 1 /2 cup heavy cream; 1 teaspoon vanilla extract; 1 /2 teaspoon kosher salt; 2 ripe but not mushy bananas, cut tcrosswise into 1/8-inch slices