Gather ingredients: strawberries, sugar, lemon juice (and pectin if using)
Wash strawberries thoroughly
Remove stems and chop strawberries
Crush strawberries to desired texture
Measure crushed strawberries and sugar according to your chosen recipe ratio
Add crushed strawberries to a large pot
Stir in sugar and lemon juice
If using pectin, add it according to package directions
Bring mixture to a full rolling boil over medium-high heat, stirring constantly
Maintain a full rolling boil for the time specified by your recipe/pectin instructions
Test for set (cold plate test or thermometer method per recipe)
Skim off foam if desired
Sterilize canning jars and prepare lids/rings
Ladle hot jam into hot jars, leaving the required headspace
Remove air bubbles and wipe jar rims clean
Apply lids and screw on rings until fingertip-tight
Process jars in a boiling water bath for the time specified for your jar size and altitude
Remove jars and let cool undisturbed until sealed
Check seals after cooling
Label jars with date and store in a cool, dark place
Refrigerate after opening and use within recommended timeframe