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In a large saucepan over medium heat saute minced garlic and chili flakes lightly in olive oil.
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Add beef broth, port wine and balsamic vinegar. Turn heat to high and cook until liquid is reduced by about half, stirring ocassionally.
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Add 3 cups of blueberries, the cinnamon and brown sugar. Cook over medium heat approximately 20 minutes or until the blueberries break apart and the sauce thickens, stirring often.
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Add the rosemary sprig and let the sauce simmer for another 5 minutes. Remove from heat.
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Add the other 1 1/2 cups blueberries and stir until berries are warmed throughout. Remove rosemary sprig.
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Spoon sauce over individual beef filets or slices of beef tenderloin and serve.