Preheat the oven to 325 °F.
Grease two loaf pans and line each with parchment paper.
Place one and one-half cups of softened butter, one package of cream cheese, and two and one-half cups of granulated sugar in the bowl of an electric mixer fitted with the paddle attachment. Beat on medium speed for three minutes, until light and creamy.
Scrape down the bowl with a rubber spatula to be sure it's well mixed.
With the mixer on low, add six extra-large eggs, one at a time, mixing well and scraping down the bowl before adding each egg.
Mix in one tablespoon of vanilla extract.
With the mixer on low, slowly add three cups of Bisquick to the butter mixture, scraping down the bowl, and paddle with a rubber spatula. Mix the batter with the spatula to be sure it's well mixed.
Divide the batter evenly between the two prepared loaf pans, smooth the tops, and bake in the center of the oven for one hour or until a toothpick inserted into the center of each cake comes out clean.
Allow the cakes to cool in the pans for twenty minutes, before turning them out and allow to cool completely on a baking rack.