In a bowl or baking dish stir together the porter, Worcestershire, onion powder and ½ teaspoon salt.
Add the filet tips and marinate for 6 to 12 hours.
Preheat the grill.
Remove the filet tips from the marinade, discard marinade.
Place the filet tips on a stack of paper towels, top with more paper towels, allow to dry for about ten minutes.
Salt the filet tips on all sides with remaining salt.
Wrap the filet tips in prosciutto, thread onto metal skewers (or pre soaked wooden skewers)
Grill on all sides until desired level of doneness, about 4 minutes per side for medium.