Combine the leaves, oil and salt in a blender, then puree on high for 60 seconds. Pour the mixture into a metal bowl set above another bowl with ice cubes and a little water, and stir the oil to cool it down and preserve the color.
Pour the oil into a container and refrigerate overnight. The next day, pour the oil into cheesecloth set over a container, and allow it to drain naturally for a few hours.
Do not press or squeeze any of the solids into the oil, or you will get water and particles that will make a cloudy oil. Pour the oil into a squeeze bottle or similar container and refrigerate.
Do not leave the oil at room temperature or it will lose it's flavor and deteriorate. The oil will keep in the fridge for a month.
Notes
Other alliaceous plants can be used here: wild onion leaves, ramp leaves, green onion tops, a mix of onion tops and herbs like tarragon, etc.