Remove the papery outer husks from the tomatillos and pierce each one with a needle or fork (optional).
Simmer tomatillos in boiling water for about 5 minutes, until they lose their bright green color.
Add one tablespoon of lemon juice to each pint canning jar (or 2 tbsp for quarts). Pack whole tomatillos into canning jars and cover with boiling water, leaving 1/2 inch headspace.
Seal with 2 part lids and process in a water bath canner for 40 minutes (pints) or 45 minutes (quarts) adjusting for altitude.
If you prefer, tomatillos can be pressure canned at 10 pounds pressure for 10 minutes instead, but pressure canning is not strictly required as they are a high acid food.
Notes
The recipe makes roughly 9 pints. The lemon juice is added to each canning jar at a rate of 1 tablespoon per pint or two tablespoons per quart. With this recipe for one canner batch of pints, you should need about 9 tablespoons of lemon juice. If you have more than 9 pints, you'll need more lemon juice. Be sure you use 2 tablespoons per jar if canning in quarts. For a standard canner batch of 7 quarts, you'd need about 14 to 16 pounds of tomatillos and 14 tablespoons of lemon juice.If you're above 1,000 feet in elevation, you may need to adjust canning times or pressures for pressure canning for all canning recipes. There is guidance on altitude adjustments here.