Place strawberries in the body of a blender or food processor and pulse (in batches, if necessary) until you have 4 cups of mashed berries.
In a VERY large heavy bottomed saucepan, combine the strawberries, sugar, and lemon juice. Stir over low heat until the sugar is completely dissolved. Increase heat to high, and bring the mixture to a full rolling boil (be careful as it does splatter…). Boil, stirring frequently, for 25 minutes; the jam will have thickened and by the end will be boiling ferociously (this is why a tall pan is very important). Transfer to clean heatproof jars, leaving 1/2 inch headspace, and let come to room temperature before placing the lid on top. If canning, follow proper canning procedures.