1. Preheat oven to 450°.
2. To prepare beef, sprinkle beef evenly with 1 teaspoon salt and peppercorns, pressing firmly to adhere. Place beef in a shallow roasting pan coated with cooking spray. Bake at 450° for 33 minutes or until a thermometer registers 135° or until desired degree of doneness. Let stand 10 minutes before slicing.
3. To prepare reduction, combine port and next 5 ingredients (through thyme) in a medium saucepan; bring to a boil. Cook until reduced to 1 1/4 cups (about 15 minutes). Strain port mixture through a sieve over a bowl; discard solids. Combine flour and 3 tablespoons water. Return port mixture to pan; add flour mixture to pan, stirring with a whisk. Bring to a boil; cook 1 minute or until thickened, stirring constantly with a whisk. Remove from heat; stir in butter and vinegar.