Over medium heat, heat the oil in a pan with a tight fitting lid that is large enough to hold all of the mussels in no more than a double layer.
Add the onion and garlic and cook until they begin to soften, about five minutes.
Add the prosciutto, broth, and mussels. Increase heat to high, and cover.
After about 3 minutes, check the mussels. If all or most of the mussels have opened up, turn off the heat. If most have not opened, replace lid and cook for another 3-5 minutes.
Scoop the mussels into a serving bowl. Use a slotted spoon to remove the prosciutto and scatter it over top. Use a ladle to pour the accumulated liquid over top the mussels, leaving behind any sediment in the bottom of the pan.
Garnish with herbs and serve with lemon wedges.
Recipe by Gutsy By Nature at https://gutsybynature.com/2016/04/12/steamed-mussels-prosciutto-garlic-paleo-aip-scd/