1. Marinate the beef. In a bowl, whisk together 6 tablespoons red wine, oil, garlic, and salt and pepper to taste; pour into a self-sealing plastic bag. Cut beef into four equal pieces; cut each piece into five or six chunks. Add beef to bag; refrigerate overnight.
2. The next day, prepare the sauce. In a heavy, deep, nonstick skillet, stir together burgundy wine, sugar, cinnamon stick and red pepper flakes. Place over medium-high heat and stir until sugar has dissolved. Simmer briskly until wine is reduced to a thin syrup, 20 to 25 minutes. (You should have about 1 1/2 cups.) Discard cinnamon stick.
3. Remove beef from bag and discard marinade. Grill tenderloin to desired doneness.
4. To serve, place sautéed spinach on serving plates; top with beef chunks, then Rioja Sauce. Top each serving with about 2 tablespoons blue cheese crumbles.
Tester's note: Sauce recipe may be cut in half. Or use this delicious sauce on pork, fish or chicken, drizzle over roasted vegetables or use as a sauce for fondue.
Per serving (beef only): 300 calories; 23g fat; 7g saturated fat; 75mg cholesterol; 22g protein; no carbohydrate; no sugar; no fiber; 45mg sodium; 15mg calcium.
Per tablespoon sauce: 24 calories; no fat; no protein; 4g carbohydrate; 4g sugar; no fiber; no sodium; no calcium.