Allium ampeloprasum var. babingtonii. Can cut tops (rather than pulling up by roots) and it will grow more leaves, with underground bulb increasing in size every year, sending up bigger tops each year accordingly. Will need thinning as it multiplies. Use in spring or early summer; dies back in midsummer after sending up flowerstalk forming top-bulbils; will send some of these bulbils.
Note: currently out of bulbils; will send in summer when new top-bulbils form.