1In a ziploc bag, add oil, beer, garlic powder, pepper, and salt. Mix together and add a pound of flank steak. Press out all air and let marinate overnight in the fridge.
2In a melted butter, add paprika, a dash of salt, and sliced onions. Cook until onions get soft.
3Take marinated flank steak out of the bag, pat dry, and broil for 5-7 minutes on each side.
4Let the steak rest.
5In a small bowl, mix warm sour cream and prepared horseradish together.
6Arrange slices of flank steak on a slice of bread.
7Top with sauteed onions, sour cream and horseradish mixture.