- FOR THE BEEF: Preheat oven to 450°F. Using tip of small sharp knife, cut slits into beef and insert garlic into each slit. Sprinkle beef all over with salt and pepper. Place beef bone-side down in heavy medium roasting pan.
- Roast beef 20 minutes. Reduce heat to 350°F. Roast until meat thermometer inserted into center of beef registers 125 degrees for medium-rare, about 1 hour 20 minutes. Transfer beef to platter. Tent with foil to keep warm.
- FOR THE RED WINE-BLACKBERRY SAUCE: pour pan juices into 2-cup glass measuring cup (do not clean pan). Freeze juices 5 minutes. Spoon fat off top of pan juices. Reserve juices; set fat aside for making Yorkshire Pudding.
- Add wine to same roasting pan. Stir over medium-high heat, scraping up any browned bits from bottom of pan. Melt butter in heavy medium saucepan over medium heat. Add onion and saute until tender, about 4 minutes. Add blackberries and cook 3 minutes. Add flour and stir to blend; cook 2 minutes. Pour red wine from roasting pan, beef broth and pan juices into blackberry mixture.
- Simmer until sauce thickens slightly, about 5 minutes. Season sauce to taste with salt and pepper.
- DETERMINING DONENESS: The internal temperature should read 110-120°F for rare, 120-125°F for medium-rare, and 130-135°F for well done.
- YORKSHIRE PUDDING:
- Sift flour and salt into large bowl. Whisk milk and eggs in another large bowl until smooth. Slowly add egg mixture to flour mixture and whisk until smooth. Cover and refrigerate until ready to use.
- When ready to bake pudding, preheat oven to 450°F. Add pan drippings to 13x9x2-inch metal baking pan. Place pan in oven and heat for 10 minutes. Reduce heat to 350°F. Quickly pour cold batter into hot pan and bake until pudding puffs and is golden brown on top, about 20 minutes. Serve immediately as it deflates quickly.