Pick healthy, pink chive flowers. Remove any insects by swishing through a bowl of water a few times. Then either drain and pat dry, or spin in a salad spinner to remove excess water. Remove stalks, and measure chives. Place in clean glass jar. For every cup of flowers, add 1 1/2 cups apple cider vinegar (ideally raw/organic). Stir, then place lid on jar and set on bench out of direct sun. Shake every now and then for 2 weeks. Decant vinegar into clean glass bottles and discard flowers. Refrigerate.
Note: make sure the vinegar is well labelled, as unsuspecting family members may mistake it for cordial!
Use the chive vinegar to make salad dressings etc, such as this French Dressing.