Jam is made by mixing fruit, pectin and sugar. For an easy strawberry jam recipe you will need strawberries, powdered fruit pectin and sugar (and you can also add lemon juice). Cut the tops off the strawberries and then mash them with a potato masher. Heat the strawberries in a pot and then add fruit pectin and sugar. Martha Stewart skips the pectin and the lemon juice and just boils strawberries and sugar together for a super easy strawberry jam recipe.