1. Heat broiler, with rack set 4 inches from heat. Line a rimmed baking sheet with aluminum foil; set aside. Soak eight 6" wooden skewers in water for at least 10 minutes.
2. Meanwhile on a work surface, chop garlic and rosemary, and sprinkle with a little salt. Press blade of knife back and forth across mixture to make a paste. Place in a medium bowl, and stir in oil; season with 1 tsp salt and 1/4 tsp pepper.
3. Cut steaks into twenty-four 1 1/2" chunks. Add to bowl; toss to coat. Thread three chunks of beef onto each skewer; place skewers onto prepared baking sheet.
4. Broil (without turning) 4-6 minutes for medium-rare. Meanwhile in a small bowl, stir together sour cream and horseradish; season with salt and pepper. Serve skewers with horseradish sauce.
