Preheat oven to 350°. In a large bowl, whisk soup, beer and sour cream until combined. Stir in potatoes, sauerkraut, cheese and chopped bratwurst. Transfer to a greased 13x9-in. baking dish. Cover and bake for 45 minutes., Uncover; bake 30 minutes. Top with pretzel pieces. Bake until bubbly and heated through, 12-15 minutes longer. Let stand 10 minutes before serving.