Leave tomatillos whole. Do not cut or attempt to deseed.
Put tomatillos in large pot, cover with water, and bring to a boil.
Simmer the tomatillos gently under just tender — about 5 to 10 minutes.
Drain tomatillos.
Pack hot tomatillos into jars, leaving 2 cm (½ inch) headspace.
MANDATORY. Acidify jars. To each half-litre/ pint jar add either 1 tablespoon bottled lemon / lime juice OR ¼ teaspoon citric acid. To each litre/quart jar add either 2 tablespoons bottled lemon / lime juice OR ½ teaspoon citric acid.
OPTIONAL: ½ teaspoon salt per half-litre / pint; 1 teaspoon per litre / quart jar.
Fill jars with fresh boiling water, leaving 2 cm (½ inch) headspace.
Debubble, top up as needed with clean boiling water from a kettle to maintain headspace.
Wipe jar rims.
Put lids on.
Process in a water bath or steam canner.
Process half-litres (pints) for 40 minutes; litre (quart) jars for 45 minutes. Increase time as needed for your altitude.