I used our common practice of using half all-purpose flour and whole-wheat pastry flour to retain a lightness to the cake, yet still impart a nutritional bonus. To impart a whisper of spice, I looked to our favorite Vietnamese cinnamon and shook just a touch over the dry ingredients to whisk in.
The wonderful pair of butter and sugar set the tone of the batter, with a splash of vanilla for its liberal floral notes. Keeping the batter from curdling and to allow the flour to be evenly absorbed, without being overworked, the dry ingredients are alternately added in with the milk needed to smooth it out. Could you skip this and just add the milk into the creamed butter mixture first? Maybe, but why not take the extra minute to give you the best result possible?
Because we wanted the top to look tidy, for extra insurance when preparing the pan, I lined the bottom with parchment paper before I started the assembly process of the cake. To prepare the rhubarb, after I sliced the stalks and scattered them into a baking pan, I doused the chunk pieces with granulated sugar to wrangle down their tartness. There isn't a ton of batter here, so to get the best coverage, we dropped dollops of it all over the top, then connected them all with an off-set spatula. It doesn't need to be perfect though, as the cake bakes, the batter will spread out and weave itself through the rhubarb, finding its way down to the bottom to hold everything together.
After baking, don't try to flip the pipping hot cake out of the pan right away - give it a ten to fifteen minute rest so it holds together. Just sweet enough, this cake was quite moist with an intriguing, shiny mosaic on top from the tender rhubarb. I didn't know if the rhubarb would play well with the cinnamon in the cake, but we were pleasantly surprised to find just how well the two work together! While I don't think this cake needed any adornment, a scoop of vanilla bean ice cream on top of a warm piece certainly didn't hurt!
Upside Down Rhubarb Cake