Melt 1 tablespoon butter in a large skillet over medium-high heat. Add shallots and prosciutto; cook until prosciutto begins to crisp, 3 to 4 minutes. Remove mixture to a plate and set aside.

Add remaining butter to the skillet and add haricots verts. Saute for 1 to 2 minutes, then add water and cover. Let green beans steam until most of the water is absorbed, about 4 minutes. Season with salt.

Remove green beans to a nice serving dish; top with the shallots and prosciutto.