Step 1

Place chopped apples, lemon, and water in a saucepan. Bring to a boil over high heat; reduce heat to medium. Cover and cook, stirring occasionally, until fruit is very soft and collapsed, about 30 minutes. Remove from heat. Strain through a fine sieve into a bowl to separate the liquid from the pulp and seeds. Press with the back of a wooden spoon or spatula to extract as much liquid as possible. Discard pulp and seeds. You should have about 1 1/2 cups pectin puree. A bit more or less will work fine.

Step 2

Place hulled strawberries in the bowl of a food processor. Pulse until berries are pureed, about 1 minute. Transfer to a saucepan. Add strained pectin puree to strawberries. Stir in 1 cup sugar. Bring mixture to a simmer over medium-high heat. Reduce heat to medium; simmer for about 15 minutes. Skim off foam. Adjust heat, if necessary, to ensure mixture is always simmering without boiling over. Stir in remaining 1 1/4 cup sugar.

Step 3

Cook, stirring often, until mixture reaches 220 degrees F (105 degrees C), 50 to 60 minutes. Remove from heat. Whisk in lemon juice.

Step 4

Ladle into sterilized canning jars while still hot. Allow to cool to room temperature uncovered. Cover and refrigerate 1 or 2 days before serving to allow sugar and pectin to thicken up the jam.