Humble fish stew showcases the underappreciated cuisine of Spain’s Balearic islands

In the shadow of an imposing stone bell tower, market stalls fan out by the dozens from the central plaza of Sineu, Mallorca.

Every Wednesday, vendors fill the surrounding streets with produce from the fertile central plain of the Spanish Mediterranean island. Interspersed among the plump tomatoes, leafy chard and bright citrus are more stalls overflowing with handcrafts, textiles, jewelry and more.

The scene plays out much like it has every week since at least the early 1200s. Designated a royal market in 1304...