In England these type of cups are know as a Noggin. Heres how i made mine. First you will have to find a tree with a burl on it, the beauty of using a burl is it is near enough shaped for you already I cut the burl from the tree using a folding saw. I trimmed off the outer bark using my knife and tided up the edges. Then i used a crooked knife to hollow out the inside of the noggin. I soaked it in oil. Very simple and strait forward to make,you can also use burl to make bowls. added some cord i made from nettles. Varnished the outside.