Start by skinning apples and chopping them and the rhubarb into bit size chunks. Quick trick, put the freshly skinned apples in a bowl of water with a lemon to a keep fresh color while you finish the prep.
Because the apples and rhubarb will cook at different temps for different times, use two pots. Fill each separately with the chopped fruit and just barely cover with water.
Put pots on the stove, pour in raw sugar to taste and bring to a low simmer. Important to note, make the rhubarb just a bit sweeter than you would like the finished sorbet to be, the flavors and sweetness will become somewhat muted once the sorbet is frozen.
Once the rhubarb is falling apart pull from stove. Pour into a food processor or use an immersion blender right in the pot. Set aside to cool once smoothly blended.
Once cool, squeeze in just a bit of fresh lemon to brighten the flavor and pour the rhubarb puree into an ice cream maker and let churn until smooth and frozen. We use Breville Smart Scoop purchased at Williams Sonoma.
While the rhubarb is churning in the machine, it will be time to take the apples off the stove as they should now be softly poached. Drain out the liquid and spread the apples on a sheet to cool and set a side. (Do not discard the liquid as it makes a delicious drink or cocktail mixer - more on that in an other post)
Once the rhubarb sorbet is frozen remove from the mixer and fold in the soft poached apple chunks. Put fresh mixture into the freezer to set for one hour.