Start by cleaning and preparing your strawberries. Remove the stems and dice them into small pieces. Similarly, peel and dice the apples into ¼-inch cubes.

In a large saucepan, combine the diced strawberries, lemon juice, and sugar. Over low heat, dissolve the sugar while gently mashing the strawberries with a wooden spoon or potato masher. This helps release their juices.

Once the strawberries are well-mashed and the sugar is dissolved, add the diced apples. Increase the heat to medium and bring the mixture to a boil.

Allow the mixture to boil, stirring frequently. Use a thermometer to check for the setting point temperature of 220°F (104°C). If you don't have a thermometer, check if the jam easily coats the back of a metal spoon. Remove from heat. The jam will continue to set up as it cools.Note: At this stage, you can store your jam in the refrigerator for up to 3 months.

Place two pint-sized mason jars in a large stockpot or water bath canner. If you don't have a canning rack, use a clean kitchen towel to prevent the jars from touching the bottom. Ensure the jars are covered by at least an inch of water. Bring to a rolling boil and boil for 10 minutes.

Using a jar lifter, carefully remove the jars and place them on a clean kitchen towel. Fill the jars with the finished strawberry apple jam, leaving ½ inch of space at the top. If you don't have a canning funnel, wipe away any residue on the jar mouth before sealing.

Secure the lids onto your jars and place them back in the hot water bath, ensuring they're covered by 1-2 inches of water. Cover the pot and bring to a boil. Let the jars boil for 10 minutes, then turn off the heat.

After 5 minutes, remove the jars from the hot water and place on a kitchen towel. Allow them to cool, undisturbed, for 12-24 hours. You should hear a popping sound from each jar, indicating a successful seal.