Whisk flour, sugar, baking soda, and 3/4 teaspoon salt in large bowl to blend. Using electric mixer, beat eggs and sour cream in another large bowl to blend. Add stout-chocolate mixture to egg mixture and beat just to combine. Add flour mixture and beat briefly on slow speed. Using rubber spatula, fold batter until completely combined. Pour batter evenly into prepared pans (about 3/4 full). Bake cakes until tester inserted into center comes out clean, about 30 minutes. Transfer cakes to rack; cool completely in the pans, then turn cake out onto rack for drizzling ganache.