This Argentinian sauce, designed to be served on freshly sliced steak, adds a delightful brightness to red meat. This sauce can be made with whatever fresh herbs you have available in your garden. You can swap out tarragon, sage or thyme for the cilantro and oregano. You can also substitute fresh chives for the shallots. If it is winter and you do not have fresh herbs, you can use dried oregano. But the fresh parsley is a MUST.