Frozen rhubarb may be used for this recipe. You will need to thaw the rhubarb in a sieve over a bowl, and squeeze and discard the extra liquid (there will be quite a bit). Once it has thawed, the rhubarb will shrink, so more frozen rhubarb will be required than fresh. If using frozen rhubarb, gently toss the rhubarb in a small amount of flour. The flour absorbs some of the liquid so it will help to distribute the fruit evenly instead of the rhubarb sinking to the bottom due to the excess liquid.