Invasive species are on the agenda right now - just ask anyone who has Japanese Knotweed growing near their property - so you can devour any edible invasive plant with great abandon. Three-cornered leek is a non-native perennial that falls into this category. Favouring shadier, damper spots like woods and riverbanks, this wild allium does all of its growing and flowering whilst most other plants have fallen dormant for the colder months. This makes it easy to find once you know what you are looking for, but it does have a knack of looking like some grasses/reeds and plants like bluebells, so identifying it can be a little tricky. The best ID features to look for are its onion-y smell and the distinctive three ‘corners’ of the cross-section of the leaf.
Although the entire plant is edible, and no council worker worth their environmental salt will stop you digging it up, the leaves and flower stems are the best for culinary use, both possessing a rich leek/onion/garlic flavour with a soft intensity that lends itself to being raw. Yes, you can use this in the same way you would regular leeks (steamed, cheesy, soups, etc.) but blitzed into a pesto is the winner here.