Yaprak mercimek is the split form of red lentils: the whole round red lentil (the "futbol" type) is broken in two, which is why it cooks faster and softens more completely. Duru sells it as a single-ingredient product, and the brand's own information page lists red lentils as the only ingredient, with Turkey as the origin.
In a Turkish kitchen this is the lentil for mercimek çorbası, the everyday soup that opens many family dinners, and it also suits mercimek köftesi, ezogelin-style soups and lentil salads; Duru itself suggests soups, köfte and salads. Rinse the lentils, simmer them with onion, carrot and a spoonful of tomato or pepper paste until they fall apart, blend if you like a silky texture, then finish with lemon and a drizzle of butter warmed with paprika.
Keep the pack in a cool, dry place away from sunlight. Duru gives the shelf life as two years.