Place the rhubarb into a bowl large enough that it can be submerged in the boiling water.
Pour the boiling water over the rhubarb to soften it. It only needs to sit for like 30 seconds. Drain the water off and squeeze it with paper towels to remove as much water as possible. Then fold it into the batter.
3 Cups Rhubarb
Butter an 8x8 baking dish and sprinkle the bottom with cinnamon sugar. Pour the batter into the baking dish.
For the Topping
Mix together sugar, cinnamon and nuts (optional) and sprinkle it over the top of the cake.
1/2 Cup Sugar, 1 teaspoon Cinnamon, 1/2 Cup Nuts
Bake for 40 minutes.
Notes
I slice the rhubarb in half lengthwise and then roughly chop them into about 1/2" pieces