Remove crust from bread. Melt 3 tablespoons butter in a medium skillet. When butter foams, add bread. Cook over medium heat until golden on both sides. Place bread on a large ovenproof platter. Spread 1/2 tbsp anchovy paste on each slice of bread. Keep platter warm in oven.
Remove butter from skillet and clean with paper towels. Melt 3 tablespoons butter with oil. When butter foams, add filet mignons. Cook over medium-high heat 2 to 3 minutes on each side or until lightly browned. Season with salt and pepper. Add 1/2 cup Marsala or sherry. Deglaze skillet by stirring to dissolve meat juices attached to bottom of skillet. Cook meat over medium heat to preferred doneness.
Place a filet mignon on each slice of bread. Keep warm.
Add remaining Marsala or sherry and cream, if desired, to skillet. Stir over high heat until sauce has a medium-thick consistency. Spoon sauce over meat.
Top with 10 to 12 very thin slices white Italian truffles, if desired. Serve immediately.