Whipped creamvanilla ice cream, or [url href="https://www.kitchentreaty.com/rhubarb-crisp-with-cinnamon-ice-cream/"]cinnamon ice cream[/url] for topping (optional)
6half-pint8-ounce canning jars with lids and screw-tops
Rimmed cookie sheetfor holding the jars while baking
Preheat the oven to 375 degrees Fahrenheit.
Wash and dry six half-pint (8-ounce) canning jars.
In a medium bowl, toss the rhubarb with the granulated sugar and 2 tablespoons flour. Divide rhubarb mixture between the six jars - each jar will fill nearly to the top with rhubarb. There will be some flour and sugar left over in the mixing bowl. Sprinkle the remaining mixture over the tops of the rhubarb. Using a long, narrow spoon or butter knife, give the rhubarb a stir to incorporate the remaining flour/sugar mixture.
In a food processor, pulse the butter, 1/3 cup flour, brown sugar, rolled oats, and cinnamon until the butter is pea-sized. You can also do this in a medium bowl with a pastry blender, two butter knives, or even your hands.
Divide the flour/oat mixture between each jar of rhubarb, sprinkling evenly on top.
Place jars on a rimmed cookie sheet and bake for 30 minutes, or until the rhubarb is tender when you poke it with a fork, and the tops are crisp and golden.
Let cool for at least fifteen minutes, or until jar is cool to the touch. You can serve after that, topping with whipped cream or ice cream if desired, or cool completely on a baking rack, add lids and tops, and store in the refrigerator for up to 3 days before serving.