1. Prepare the Crust:

1. Preheat the oven to 350°F (175°C) and grease a 9×5-inch loaf pan.
2. In a large bowl, cream the butter and sugar until light and fluffy. Mix in the eggs one at a time, then stir in the vanilla extract.
3. In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add to the batter alternately with the buttermilk and sour cream, beginning and ending with the flour mixture.
4. Pour the batter into the prepared pan and bake for 60-70 minutes or until a toothpick inserted into the center comes out clean. Let cool in the pan for 10 minutes, then turn out onto a wire rack to cool completely.
5. To make the caramel icing, combine the brown sugar, cream, and butter in a saucepan over medium heat. Bring to a boil and let it cook for 1 minute, then remove from heat and stir in vanilla.
6. Pour the caramel icing over the cooled cake.