Rhubarb Upside-Down Cake
Let the cake cool for 10 minutes before removing it from the pan. The rhubarb will be too hot to handle safely right after baking. But if the cake sits much longer, it may stick.
On "Martha Bakes," Martha doubled the amount of crumb topping and used 1 teaspoon finely grated lemon zest and 1 tablespoon fresh lemon juice instead of orange zest and juice in the cake.