1. Preheat oven to 350 degrees F and grease or line a 9x13 baking dish with parchment paper. Set aside.

Mix

1. Whisk the milk, sourdough discard and vanilla in a small bowl until combined. Set to the side.
   120 grams milk, 240 grams sourdough discard, 4 grams vanilla extract
2. In a bowl of a stand mixer with a paddle attachment, cream the butter and sugar for about 2 minutes.
   113 grams unsalted butter, room temperature, 350 grams sugar
3. Add the egg to the sugar mixture and beat until fluffy with a pale yellow color, for about 3 minutes.
   1 large egg

Dry Ingredients

1. In a medium bowl, whisk together the flour, baking soda and salt.
   150 grams all-purpose flour, sifted, 6 grams baking soda, 3 grams salt
2. Alternate adding the dry ingredients and wet ingredients. Add about a third of the flour mixture, then half of the liquids. Repeat until all of the ingredients have been added and the flour bits have just disappeared. (Note that the batter is on the thicker side)

   Be sure to not overmix the cake batter - this can lead to a tough crumb.
3. Lastly, fold in the bits of rhubarb.
   240 grams rhubarb, 1/2 inch slices

Bake

1. Pour the batter into the baking dish. You can even top it with more pieces of rhubarb.
2. In a separate bowl, mix together the sugar and cinnamon. Sprinkle on top of the batter - make sure to get all the edges of the cake.
   50 grams sugar, 1 gram ground cinnamon
3. Bake for 40-45 minutes or until a toothpick comes out clean.
4. Let the cake cool on a wire rack before slicing and enjoy!