This is an easy treat! Slice rhubarb, add some water, sugar (I used about 11/2 cup for about 4-5 cups fruit). Then simmer gently until rhubarb is tender. Turn off the heat and add the raspberries. I served it with home made crime fraiche: heavy cream with some buttermilk, let it sit out overnight.
I like the rhubarb to retain some texture, so didn't slice too thinly.
Add some water, sugar, simmer. It doesn't take long.
I added the raspberries at the end, turned off the heat.
I put some heavy cream (not ultra pasteurized) in a jar, almost to the top, then added buttermilk. I set it in a pan of warm water to start with, then just left it out on the counter overnight to thicken. It is yummy!