Bring a medium sized pan of water to a brisk boil.

Plunge a bushy sprig of French tarragon into the boiling water for 10 seconds (“blanch”).  Remove and plunge immediately into cold water to “refresh” it.

Dry thoroughly on some kitchen towel.

Open a fresh bottle of (Apple) Cider Vinegar (usually 350ml in the UK) and pour out a couple of tablespoons to make room.  Ease in the blanched tarragon and screw the lid back on tightly.

Invert the bottle a few times to mix and leave in a cool, dark place to infuse for at least a month before using.

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Use in a dressing or mayonnaise for simple poached chicken or fish dishes, warm new potatoes or french beans.  Yum!