Preheat the oven to 325°F. Spray two 8-inch round baking pans OR a 9x13-inch baking pan with baking spray. If using round cake pans and you want to serve the cake on a platter or plate, line the bottom with parchment paper.
Bake the cake for 40-50 minutes (for 9x13-inch pan) and 30-40 minutes (for the 2 8-inch cake pans) or until a cake tester or toothpick inserted into the center comes out clean, or with just a few wet crumbs clinging to it. The temperature at the center of the cake will be about 205°F.
Heat 8 tablespoons butter, brown sugar, and salt in a large saucepan over medium heat until small bubbles appear around the perimeter of pan 5-7 minutes. Whisk in cream and cook until a ring of bubbles reappears about 1 minute. Off heat, whisk in vanilla.
Allow mixture to cool in the pot for 15 minutes (it should be warm but not hot), then add 3 cups of the powdered sugar and, using a whisk, stir until smooth and creamy, about 1 minute. Add more powdered sugar, if needed and whisk to make a thick but spreadable icing. Add remaining 4 tablespoons soft butter, and whisk again until light and fluffy, about 1 minute.
If frosting both round cakes transfer icing to the center of the cakes and, working with an angled metal spatula or a knife, spread the icing outward, stopping at the edges and swirling the icing as desired. If frosting the 9x13-inch cake, transfer icing to the center and working with an angled metal spatula, spread the icing to the edges, swirling as desired. Work fairly quickly as the icing will harden once it reaches room temperature. If it hardens too much before you get a chance to spread it, simply warm it in the pot for 30 seconds to 1 minute over low heat.
The frosting recipe is for two cake 8-inch round cake or one 9x13-inch cake. I often serve one cake and freeze the other. I just make half of the icing for the cake I'm serving and then I make fresh icing when I defrost the second cake
See Café Tips above in post for further instructions and more detailed tips.
Cake recipe adapted from King Arthur Flour
Icing recipe adapted from Cook’s Country