Start by peeling and finely dicing the peaches. Dice the strawberries as well, removing the stems. Measure out 5 cups of peaches and 4 cups of strawberries. Set aside.

In a large, heavy-bottomed pot, combine the peaches and strawberries. Place over medium heat and bring to a gentle boil, stirring often to prevent sticking or burning. Once boiling, reduce the heat slightly and let the mixture simmer for 30 minutes, continuing to stir occasionally. The fruit will begin to break down and release juices.

After 30 minutes, stir in the sugar, lemon juice, and dry pectin. Mix well to fully dissolve the sugar and pectin into the fruit mixture.

Increase the heat and bring the jam back to a rolling boil, stirring constantly. Continue boiling for about 5 minutes, or until the jam reaches 220°F on a candy or instant-read thermometer. This is the setting point that helps the jam firm up properly.

Remove the pot from the heat. Carefully ladle the hot jam into warm, sterilized jars, leaving about ¼ inch of space at the top. Wipe the rims clean, place the lids on, and screw the bands on until fingertip tight.

Place the filled jars in a boiling water bath, making sure they are fully submerged. Process for 10 minutes to seal. Once done, carefully remove the jars and let them cool undisturbed on a towel or cooling rack for 12 to 24 hours.

Once cooled, check that the lids have sealed (they should not flex when pressed). Label your jars and store them in a cool, dark place for up to a year.