Start by combining the chopped apples, strawberries, and rhubarb in a large saucepan.
4 cups apples, 1 cup strawberries, 1 cup rhubarb
Add sugar, cinnamon (if using), and water to the fruit mixture.
1/4 cup sugar, 1 teaspoon cinnamon, 1/2 cup water
Bring the mixture to a gentle simmer over medium heat, stirring occasionally to prevent sticking.
Reduce the heat to low and cover the pan partly, letting it cook for about 15 minutes until the fruits soften and release their juices.
Uncover the pan and stir the mixture, mashing occasionally with the back of a spoon for a chunkier texture or more until smooth if desired.
Continue cooking for another 5 minutes until the sauce thickens slightly and becomes fragrant.
Remove from heat and let it cool slightly before serving, or transfer to jars for storage.