Roasting is one of the easiest yet most flavorful ways of cooking cauliflower. The flavors concentrate during the roasting, bringing out savoriness and depth of flavor with the simple addition of olive oil. I often serve roasted cauliflower just like that. It’s so easy! But to turn it into a rustic hors d’oeuvre, I serve it with romesco sauce for dipping.  Romesco is a thick tomato and roasted red pepper sauce originally from Catalonia, Spain. It is traditionally served with calcots, a local green onion that resembles a small leek or a large scallion. The dish is served but once a year to celebrate the harvest in late February. Farmers and growers gather around a bonfire, char the calcots over the open fire, peel them, and then dip them in the romesco sauce.  But here, as open bonfires are frowned upon, I am roasting cauliflower florets in the safety of …