What French cheese is known for its blue veins and strong flavor?

The French cheese known for its blue veins and strong flavor is Roquefort.

Roquefort is a blue cheese made from unpasteurized sheep's milk in southern France. It takes its name from Roquefort-sur-Soulzon, a village in the Aveyron region where the cheese is aged in the natural Combalou caves.

The caves provide cool, humid conditions that help the mold Penicillium roqueforti develop. Cheesemakers pierce the wheels to introduce oxygen, allowing the mold to grow through the interior and form Roquefort's distinctive blue-green veins. The mold and the breakdown of milk fats contribute to its sharp aroma and tangy, intense taste.

Roquefort is often confused with blue cheeses such as Stilton or Gorgonzola, but those are different varieties made in other regions and often from different types of milk. Under European geographical-protection rules, only cheese aged in the caves at Roquefort-sur-Soulzon may legally use the name Roquefort.