Last summer I was tied to Alice Waters' The Art of Simple Food cookbook. This summer I can't stop making stuff out of Rachel Allen's Favorite Food. Since rhubarb is currently in season, I snatched up a bundle of stalks and decided I'd figure out what to do with them when I got home. Luckily, Allen had a tasty recipe for Upside-down Rhubarb Cake.
This recipe was super easy. Chop up the rhubarb, melt some butter in a cast iron pan, mix up the ingredients, and pour it all in. My cast iron pan is too wide for my cake plate, so I used a 9" cake pan instead, melting the butter in the oven rather than on the stove top. You can find the recipe here. If you prefer grams and milliliters over cups, here is the recipe from a UK food website.
This cake is super moist, so if you aren't going to eat all off it in a day, I would suggest putting it in the fridge. We left ours out under a cake dome in our kitchen and it molded in 3 days due to the moisture from the cake. Lesson learned!