Cut shallow slits all over roast. Insert garlic slivers into slits. Rub all over with coarse salt and pepper. Place, fat side up, on rack in shallow roasting pan (no water is necessary). Insert oven-safe meat thermometer into centre of roast, avoiding fat or bone. Oven-sear by placing uncovered roast in preheated 450°F oven for 10 minutes.
Reduce heat to 275°F. Cook until thermometer reads 145°F for medium-rare, about 2-1/4 to 2-3/4 hours. Remove from oven.
Place roast on cutting board. Cover with foil and let stand for at least 15 minutes. Carve roast into thin slices and serve with sauce and Yorkshire puddings.
Peppercorn Wine Sauce
Put pan drippings and green onions in roasting pan over medium-high heat. Stir in 2 tbsp all-purpose flour. Cook, stirring constantly, for 1 minute. Gradually stir in 1 cup each of beef broth and red wine, and 2 tsp cracked mixed peppercorns.
Cook, stirring up any browned bits from bottom of pan. Whisk until sauce boils and thickens, about 4 minutes.
Make ahead. In medium bowl, combine 1 cup flour and 1/2 tsp salt. Add 1 cup milk and 2 eggs. Beat with mixer just until smooth.
Cover and refrigerate until ready to cook (allow batter to return to room temperature before using).
To cook: pour a bit of the reserved fat from the roast into each cup of a 12-cup muffin pan. Heat the pan in 425°F oven for 5 minutes. Divide Yorkshire pudding mix among the muffin cups and bake 15 to 20 minutes until golden brown. Serve immediately.
Toss thin slices of cooking onion in corn starch that's been seasoned with a bit of salt and pepper. Pan fry in batches about 1/4-inch sizzling hot canola oil, turning until crisp and golden, 2 to 3 minutes.
Using a slotted spoon, remove to paper towel-lined plate to drain (can be made ahead up to 2 hours, storing at room temperature).