Mixed Root Remoulade

I once worked in a frightfully lah-di-dah restaurant that used to blanket all manner of food with mayonnaise and then call it remoulade. I used to think they made it up, but as it turns out, it’s a thing: remoulade is basically just mayonnaise with stuff up it. In France, celeriac remoulade is practically a national institution. This version adds a few Peckham spices, and mixes up the tubers so that if you can’t find one, you can use something else.