Leave root and 1 inch stem on beets; scrub with a brush. Place beets in an 8-inch square glass or ceramic baking dish; add water to a depth of 2 inches. Cover with foil; bake at 425° for 50 minutes or until just tender. Drain and cool. Peel beets; cut into 1-inch wedges. Place beets in a large heatproof glass jar or bowl with peppercorns and thyme.
Combine raspberries and remaining ingredients in a medium saucepan. Bring to a simmer; cook 4 minutes, stirring occasionally, until sugar dissolves and raspberries begin to break down. Strain raspberry mixture through a fine sieve over a bowl; discard solids. Pour hot raspberry liquid over beet mixture; cover and chill at least 8 hours or overnight.
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