Add diced apples to a large bowl. Sprinkle with sugar and lemon juice, gently stir to combine. Cover bowl and place it in the fridge for at least 4 hours or overnight for best results.

Drain the macerated fruit in a large fine mesh sieve over a jam pot or saucepan.

Bring the leftover liquid from the fruit to a boil in the saucepan.

Add the diced apples to the boiling liquid. Reduce heat to medium-high and cook for 20 to 30 minutes or until the desired texture is achieved. Stir occasionally to prevent scorching.

Pack prepared jars with hot jam, leaving 1/4-inch headspace. Debubble the jam with a spatula or chopstick and adjust headspace as needed. Apply two-piece canning lids until fingertip tight.

Load jars into a hot bath canner and process for 10 minutes. When the timer goes off, turn off the heat and let the jars sit in the hot water for another 5 minutes.

Remove jars from water canner and transfer to a clean surface lined with a kitchen towel, leaving 1 inch of space between each jar. Let the jars come to room temperature.

Test the seal on each jar, storing any improperly sealed jars in the fridge for 1 to 2 weeks. Sealed jars of apple jam can be stored in a cool, dry location away from direct light for up to 18 months.