Soak the peas overnight in deep cold water.
The next day drain, cover with fresh water and bring them to the boil.
Turn the heat down and let them simmer with the onion, mint and a glug or two of olive oil.
After an hour or so they will be tender enough to crush against the side of the pan. If not, cook them for a while longer.
If they are no longer covered by water, then add some boiling water to top them up.
Remove all but a third of the peas and water and put it in either a blender or a food processor til smooth.
Return the smooth mixture to the pot, and cook for a few minutes until it thickens.
To make the butter, mash all the ingredients together with a generous teaspoon of salt and then chill.
Ladle the soup into bowls and stir a wodge of spiced butter into each one.
Serve with some nice warmed bread.
