Immerse the mushrooms in cool water and clean them meticulously. See note on if your mushrooms are perfectly clean in the recipe notes.
Gently crush the juniper berries with the back of a knife to release their aroma.
Combine all ingredients in a small sauce pot and bring to a boil.
Cook for 2-3 minutes until the chanterelles are wilted. If you have a lid for the pot covering it will speed up the process.
When the mushrooms are wilted and completely cooked, transfer them to a pint mason jar, cover the mushrooms completely with pickling liquid, cover with a lid and refrigerate.
The mushrooms will last for a long time in the fridge, check on them occasionally to make sure they're underneath the pickling liquid.
For long term storage, the mushrooms can be water bath canned. To do that, process pint jars for 10 minutes in a water bath canner.
Video
Notes
Soaking the chanterelles is something I only do with young buttons and it directly affects the water content of the finished pickle as they absorb about 4 oz of water. If your chanterelles are pristinely clean you can skip soaking them, but you'll need to increase the water in the recipe to a full cup (8oz).