So, I searched French sites for "sauce vierge recette" and they all have a recipe
for an olive oil based sauce. Except I found this one which is for
"SAUCE MOUSSEUSE, DITE AUSSI BEURRE À LA VIERGE" translated means
"FOAMY SAUCE, ALSO KNOWN AS BUTTER VIRGIN"
http://www.cuisineetvinsdefrance.com/,sauce-mousseuse-dite-aussi-beurre-a-la-vierge,54606.asp
So then I searched for "BEURRE VIERGE" and I got a couple of hits for a butter based sauce..