The document Buenchico linked to is fascinating but I was foxed by a comment about holding a spoon such that the thumb goes under the handle.
I'm convinced this is a typo. I find this restricts the freedom of motion of my hand and weakens the grip. I have the thumb on top, gripping the handle against the forefinger, enabling the edge of the spoon to cut a piece off the dessert and then scoop the piece up. Whereas the fork would be left hand, tines curving down, the spoon is left hand, concave side up. Otherwise, same grip.