Double Banana Cake

Name: Double Banana Cake
Ingredients: 1½ cups (3 sticks) unsalted butter plus more for pans, room temperature; 3¾ cups all-purpose flour; 1½ teaspoons baking soda; 1¼ teaspoons kosher salt; 2¼ cups sugar; 6 large eggs; 3 cups coarsely mashed very ripe bananas (about 6 large); ¾ cup sour cream; 1 cup (2 sticks) unsalted butter, room temperature; 4 cups powdered sugar; ½ cup heavy cream; 1 teaspoon vanilla extract; ½ teaspoon kosher salt; 2 ripe but not mushy bananas, cut crosswise into ⅛-inch slices