Preheat oven to 350 degrees. Toss garlic cloves and oliv oil in small baking dish, cover. Bake until garlic begins to rown, about 35 minutes. Drain olive oil into processor. Cool 15 minutes. Peel garlic'place n processor, add prepared horseradish and coarse salt. Puree until almost smooth.
Place rack on large rimmed baking sheet. Sprinkle beef with salt and pepper. Spread thin layer of garlic mixture on underside of beef. Place beef, garlic mixture side down onto rack. Spread beef with remaining garic mixture. Cover and refrigerate at least 3 hours or up to 1 day. Position rack in bottom third of oven; preheat to 350 degrees. Uncover beef. roast until thermometer inserted into top center registers 130-135 degrees. Let stand for 30 minutes prior to carving.
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