I do not have access to calcots, nor have I ever tried them before. I have heard that they are a cross between a scallion and a leek (not an exact definition). Which would you consider to be an appropriate substitution for grilling and serving w/romesco?
We have a wide variety of scallions out here, some as big as my thumb and they have a fairly robust onion flavor, so I figured they'd work out just fine. Leeks, IMHO, are far too mild in flavor to provide anything more than a vehicle for carrying the sauce to the open mouth.