Plomeek soup or Plomeek broth was a Vulcan food. It was usually described as bland in taste, although variations such as a spicy version existed. It was considered a traditional morning meal on Vulcan. (ENT: "Unexpected")
Plomeek broth and soup was commonly offered aboard Enterprise, including among a breakfast spread in 2151. T'Pol was rarely interested in experimenting with Human food, and tended to prefer plomeek options. (ENT: "Unexpected") When Hoshi Sato was in charge of the galley in 2152, she claimed that she was too busy for "special orders", such as T'Pol's request for plomeek broth, and that she would like that night's prepared dish, oden, better. (ENT: "Singularity")
In 2267, Nurse Christine Chapel made the mistake of serving it to Spock during his pon farr. Spock tossed the bowl at her, causing a public scene. Later, he apologetically asked if she would prepare it for him again. (TOS: "Amok Time")
In 2370, while in a holographic program on the USS Enterprise-D set in 2161, William T. Riker, assuming the role of Enterprise's chef making some of the crew's favorite foods one last time, started preparing Commander T'Pol's plomeek broth before Enterprise reached Rigel X. (ENT: "These Are the Voyages...")
Julian Bashir often ordered plomeek soup. In early 2371, he ordered it with a touch of basil. Later that year, he ordered it when he and Miles O'Brien had lunch. (DS9: "The House of Quark", "The Die is Cast")
In 2377, Neelix offered Ensign Harry Kim a choice of eating eggplant parmesan or plomeek soup, shortly before Kim left to take command of a Kraylor vessel he would later dub Nightingale. Kim replied that either food was fine with him, until Neelix advised him that a commanding officer should be decisive, leading Kim to choose the plomeek soup. (VOY: "Nightingale")
Plomeek (β) is presumably a plant (or a part of a plant) indigenous to Vulcan, though it has never been seen or described separately from the soup, broth, or tea on screen.
The Hidden Universe Travel Guide: Vulcan (p. 86) identifies the plomeek as a flowering plant common across Vulcan's temperate regions, with the "verified record holder for largest plomeek" being at T'Pran's Market in Raal at eight meters tall.
The Way of Kolinahr (p. 12) notes that plomeek soup has many regional varieties.
It is also referenced in the novels The Sundered, The IDIC Epidemic, The Better Man, Rough Beasts of Empire, Precipice, Requiem, A Time to Sow, Preserver, No Limits, Her Klingon Soul, Being Human, Saratoga, The Eyes of the Beholders, Cybersong, Last Full Measure, A Singular Destiny, Dark Matters, Assignment: Eternity, The Empty Chair, Summon the Thunder Academy: Collision Course, The Rise and Fall of Khan Noonien Singh, Volume Two, and Captain's Blood.