Slit the prawns down the back, open them like a butterfly and remove the vein.
Heat the oven grill.
Melt butter in a shallow baking dish, and mix in the olive oil, with lemon juice, garlic, salt and pepper.
Dunk in the prawns in the mixture, coat well and place them side by side, shells down.
Grill for 5 minutes or until well cooked.
Place the hot prawns on a serving platter, pour the sauce over it and decorate with lemon wedges.