Preheat Oven and Prepare Pan: Start by preheating your oven to 325°F (165°C). Grease and flour your loaf pan thoroughly to prevent sticking.
Cream Butter and Sugar: In a large bowl, use an electric mixer to cream the butter and sugar together until light and fluffy.
Add Eggs: Add eggs one at a time, beating well after each addition.
Mix Dry Ingredients: In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add this to the creamed mixture, mixing on low speed.
Add Flavorings: Stir in the Hennessy cognac and vanilla extract. Mix until just incorporated.
Add Sour Cream: Fold in the sour cream until the mixture is smooth.
Bake: Pour the batter into the prepared pan and smooth the top with a spatula. Bake for 60 to 70 minutes or until a toothpick inserted into the center comes out clean.
Cool: Let the cake cool in the pan for 10 minutes, then turn out onto a wire rack to cool completely.