Having a large group for Christmas dinner and bought a 11 lb sirloin roast. I have read to braise it and then cook in a low temp oven for 1 1/2 hrs per pound. Also read put in oven at 500 degrees for short time then lower temp. I am so confused.... I know that I need to use a meat thermometer. At what temp do I need for medium rare? And what seasonings do I use? What about using a baking bag?