Preheat oven to 300 degrees Fahrenheit and thoroughly grease and flour a 12-cup bundt pan or tube pan. Tap out excess flour and set aside.
In a large mixing bowl, or stand up mixer fitted with paddle attachment, combine the butter and mascarpone cheese. Beat together using an electric mixer or paddle attachment on high speed until light and fluffy.
Add in the sugar and mix again, increasing speed to high and beating until light and fluffy. Scrape the bottom and sides of bowl to make sure all of the ingredients are well incorporated.
Add in the eggs, one at a time, mixing between each addition. Add in vanilla and mix to combine.
In a separate medium sized bowl, whisk together flour, salt, and baking soda. Gradually add dry ingredients to wet, stirring until completely combined. Once combined, beat on medium speed for another minute until batter is smooth and light.
Pour pound cake batter into prepared pan. Bake on the center rack in oven for 95-100 minutes, or until a wooden skewer inserted into the center of the cake comes out clean or with moist crumbs.
Allow the cake to cool in pan for 10-15 minutes on a wire cooling rack. Then, carefully invert onto the cooling rack to cool completely. Make sure cake is completely cooled before cutting with a serrated knife and serving.