Prepare water bath canner, pints jars, lids, and bands. Lids and bands should be placed in simmering water. Jars should be heated but do not need to be sterilized.
Puree the strawberries in a food processor fitted with the metal blade until liquified. Some seeds may remain but there should be no berry chunks. Transfer the strawberry puree into a large stainless steel (or other non-reactive) saucepan.
Add the lemon juice and sugar, and stir to combine. Heat mixture over medium heat until it reaches 190-200 degrees. Do not boil, just heat. If any foam forms, skim it from the surface using a large spoon.
Fill clean, hot pint jars with the lemonade concentrate, leaving 1/4 inch of headspace. Carefully remove lids and bands from the simmering water and fasten to be fingertip tight. Lower into boiling water canner, and process for 15 minutes at a full boil with the lid on.
Remove cans and allow to sit undisturbed on counter for 12-24 hours or until jars seal. When the lids are pressed, they should be firm and not move at all. Any jars that have not sealed can be placed in in the refrigerator and used within 2 weeks. Store sealed jars in a cool, dark place for up to 2 years.