Step 1

Preheat the oven to 350°F

Step 2

Liberally grease a 9 or 10 inch cast iron skillet, or other pan of similar size, with half of the butter.  (Yes, half!  It would be sad if your cake stuck to the pan).

Step 3

Sprinkle the bottom of the skillet with the brown sugar, then add the rhubarb slices in a single layer.

Step 4

Whisk together the remaining butter, yogurt, eggs, vanilla, and sugar.

Step 5

In a separate bowl, combine the flour, baking soda, salt, and cinnamon.

Step 6

Add the liquid mixture to the flour mixture, and stir gently to combine.

Step 7

Pour the batter into the skillet, on top of the rhubarb, smoothing and leveling the top.

Step 8

Bake for 50-60 minutes, or until a toothpick stuck in the center comes out clean. Let cool for about 5 minutes.

Step 9

Gently run a knife around the edge of the cake to loosen it from the skillet. Put a plate that is larger than the skillet over the top. Using hot pads (I highly recommend a hot handle holder for cast iron skillets), carefully flip the cake over and gently lift the pan off the cake.