Preheat your oven to 325°F (163°C). Grease and flour your loaf pan to ensure the cake doesn't stick.
In a large mixing bowl, combine 1 cup of softened unsalted butter and 1/2 cup of shortening. Beat them together until the mixture is light and fluffy.
Gradually add 3 cups of granulated sugar to the creamed mixture, beating well after each addition. Next, add the 5 large eggs, one at a time, ensuring each egg is fully incorporated before adding the next.
In a separate bowl, whisk together 2 1/4 cups of all-purpose flour, 3/4 cup of unsweetened cocoa powder, 1/2 teaspoon of baking powder, and 1/2 teaspoon of salt.
Dissolve 2 teaspoons of instant coffee or espresso in 1/4 cup of hot water. Add this mixture along with the 1 cup of buttermilk and 1 tablespoon of vanilla extract to the creamed mixture. Mix well.
Gradually add the dry ingredients to the wet mixture, mixing until just combined. Be careful not to overmix!
Pour the batter into the prepared loaf pan and smooth the top. Bake in the preheated oven for 60-70 minutes or until a toothpick inserted in the center comes out clean.
In a saucepan, combine 1 cup of heavy cream and 1 (16-ounce) box of light brown sugar. Bring to a boil over medium heat, stirring constantly. Once it reaches a boil, reduce the heat and let it simmer for about 5 minutes. Remove from heat and add 1/2 teaspoon of baking soda and 1/2 cup of butter cut into 8 pieces, stirring until smooth.
Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack. Once completely cooled, pour the warm caramel icing over the top of the cake, letting it drip down the sides.