Toss shallots and 2 tablespoons oil in a bowl; stir in 3/4 teaspoon salt and 1/2 teaspoon pepper. Set aside.
Stir together 1 tablespoon salt and next 4 ingredients. Rub tenderloin with 1/4 cup olive oil; sprinkle seasonings over top and sides of tenderloin, pressing gently with fingers. Place tenderloin in a large greased roasting pan; arrange shallots around tenderloin. Bake, uncovered, at 500° for 25 minutes. Reduce oven temperature to 375°, and bake 15 to 20 minutes or until meat thermometer inserted into thickest part of roast registers 145° (medium-rare) or 160° (medium).
Meanwhile, stir together beef broth and Marsala in a large skillet. Bring to a boil; boil 6 to 8 minutes or until liquid is reduced to 2 cups.
Remove tenderloin to a serving platter and cover with aluminum foil; reserve shallots and drippings in pan. Add broth reduction to pan, and place over medium heat on cooktop, stirring to loosen particles from bottom of pan.
Whisk together flour and water until smooth; stir into sauce in roasting pan. Cook over medium heat, stirring constantly, until slightly thickened. Add butter, stirring just until melted. Stir in 1/4 teaspoon pepper. Thinly slice roast, and serve with sauce. Garnish, if desired.
For Entertaining, Wine & Dine: We recommend any of these wines with dinner: Morgan Monterey Syrah, Chateau Souverain Dry Creek Zinfandel, or Bleasdale Langhorne Creek Shiraz-Cabernet.