Rhubarb Upside-down Cake
from https://www.thekitchn.com/

You’ve probably associate upside-down cakes with pineapple, but there are plenty of other fruits that deserve the upside-down treatment. Our current favorite is fresh rhubarb, in all its vibrant pink and sweet-tart glory.

This recipe takes advantage of fresh, in-season rhubarb to create a stunning upside-down cake that’s both beautiful and delicious. Stalks of rhubarb get nestled into a mixture of butter and sugar, then get covered in a simple cake batter and baked. The cake won’t look like much when it comes out of the oven, but once you invert it onto a serving plate, the bright pink streaks of rhubarb reveal themselves, making for a seriously impressive presentation.

How to Prevent Your Upside-Down Cake from Sticking

This recipe uses three techniques to prevent your cake from sticking to the pan. You’ll coat the cake pan in nonstick cooking spray, line the bottom with parchment paper, and give the cake just enough time to cool without the sugar hardening.

The cooling time is arguably the most important factor. You want the cake to cool long enough to firm up before flipping, but not so long that the bottom layer hardens and sticks to the pan. For this recipe, we found that 20 minutes is the right amount of time. Set a timer as soon as the cake comes out of the oven and it will come out perfectly every time.

1 pound rhubarb
1/2 cup brown or granulated sugar
1/3 cup melted butter
1 (15.25-ounce) box your favorite yellow or white cake mix (or make your own, see Rich Yellow Cake - follow instructions for 9" square pan)
3 large eggs
1/2 cup vegetable oil
1 cup water

Preheat oven to 350 °F

Wash and trim rhubarb stems at least ½" thick. Grease sides and botom of 9" square cake pan, then line the bottom with a parchment paper round.

Pour the melted butter into the bottom of the prepared baking pan and sprinkle with 1/2 cup granulated sugar. Nestle 1 pound rhubarb, rounded-side down, into the sugar in an even layer without overlapping, trimming the rhubarb as needed to fit.

Place 1 box cake mix, 3 large eggs, 1/2 cup vegetable oil, and 1 cup water in a large bowl and whisk until smooth. Pour over the rhubarb and smooth out the top.

Bake until the cake is lightly browned and a toothpick inserted into the center comes out clean, 20 to 25 minutes.

Place the pan on a wire rack and let cool for 20 minutes. Remove the warm cake from the pan by running a knife around the edge and gently inverting it onto a serving plate. Discard the parchment paper before slicing.

Yields one 9" x 9" cake