- In a small bowl, combine the garlic, mustard, olive oil, thyme and pepper.
- Pat the beef dry with paper towels, then spread the prepared mustard mixture over the surface. Let stand at room temperature for 1/2 hour. Meanwhile, prepare the barbecue by placing a drip pan under the cooking grids. Fill halfway with hot water, then preheat the barbecue on MEDIUM. Adjust the heat to MEDIUM/LOW, and place the prime rib on the cooking grids. Close the lid, and cook about 15 minutes per pound for medium rare. Using a meat thermometer to check doneness is a must. An initial check after an hour or so will give you a chance to assess the timing of the other dishes.
- Closely monitor the level of water in the drip pan, ensuring it never runs dry. Very carefully add hot liquid to the drip pan as necessary, taking care to protect your hands with oven mitts to prevent steam burns.
- When the meat is almost at the desired doneness, remove the roast from the barbecue and place it on a carving board tented with foil. Let it rest 20 minutes before carving. Refer to the Indirect Cooking Guide
- Béarnaise Sauce: In a small saucepan, combine vinegars, water, shallots, tarragon and cracked black pepper, and bring to a boil over MEDIUM/HIGH heat until reduced to one tablespoon. Reduce temperature to LOW and whisk the egg yolks into the reduction. Whisk in the butter one cube at a time, waiting until the butter is incorporated before each addition. Continue whisking until thickened. Season with salt and cayenne.
Recipe from Gathering Around The Grill Cookbook