Sara, I assume there's sugar in this cake that you failed to list. I'd beat the butter, shortening, and sugar together at medium speed (speed #4 for the KitchenAid) until lightened in color; this should take maybe 4-5 minutes or so. Add the eggs one at a time, scraping the bowl and mixing thoroughly after each. Add the vanilla; then whisk the flour with the baking powder and salt, and add it, 1 cup at a time, to the egg mixture, alternately with the milk. Do this all at lower speed (speed 2 is fine), and beat only until the mixture smoothes out each time. There's no need to beat this cake batter for 30 minutes; perhaps, if it originally lacked chemical leavening (baking powder; many older pound cake recipes don't include baking powder), it needed 30 minutes of beating to lighten and aerate the eggs/sugar/butter. But this isn't necessary, considering the baking powder. Good luck! PJH

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