The Catalan dish featuring grilled spring onions served with romesco sauce is calçots.
Calçots are a specially cultivated type of green onion or spring onion associated with Catalonia, particularly the area around Valls in Tarragona. They are grown by gradually covering the shoots with soil, a process that blanches the lower stalk and encourages a long, tender white portion.
For a traditional calçotada, the onions are grilled over a very hot fire until their outer layers are blackened. They are often wrapped briefly so they steam, then diners peel away the charred exterior by hand and dip the tender center into a nutty, garlicky sauce.
Romesco is commonly named as the accompaniment, though Catalan cooks may distinguish it from salvitxada, or salsa de calçots. The sauces are closely related but can differ in ingredients and texture. The meal often continues with grilled meats, bread, and wine.
The term calçot can refer to the onion itself, while calçotada means the communal barbecue or feast centered on it. That distinction explains why both names appear in descriptions of the dish.