Drain all but 1 tablespoon drippings from Dutch oven; place back on medium heat. Add onion; cook about 6 minutes, stirring occasionally, until softened. Add garlic; cook 1 minute. Add potatoes, stock, salt and pepper. Increase heat to medium-high. Heat to boiling. Reduce heat to medium-low; simmer 10 minutes. Add rosemary sprigs; simmer 10 minutes.