Sweet and tart, tender and delicious, this sourdough rhubarb snack cake is full of summer flavors perfect for a summer party or to enjoy on spring day.
To a medium sized bowl, beat together butter, sugar and lemon zest until light and fluffy. Add the egg and beat again until fully incorporated. Add the sourdough discard, sour cream and vanilla extract. Beat together until incorporated.
To the middle of the mixture (or in a separate small bowl), add the flour, baking powder and salt. Lightly fluff the baking powder and salt into the flour with a fork (if mixing in a bowl, add it to the wet mixture now) and mix until just combined.
Scoop the batter into the prepared pan and gently spread into an even layer using an offset spatula or the back of a spoon. Pour the prepared rhubarb mixture over the cake batter, creating an even layer as best you can.
Stir together the crumb mixture: melt the butter and add the brown sugar, flour, salt and sprinkle of cinnamon. Once it comes together, use your fingers to spread chunks of crumb topping evenly over the rhubarb layer.
Bake in preheated oven for 50-60 minutes. The cake is finished when a toothpick is inserted into the cake and comes out clean--no wet cake batter. Cool completely and then remove the cake (using your parchment sling) and cut into pieces to serve. Enjoy!
Notes
Sourdough Discard:Not all sourdough discard is created equal. Discard that has been sitting in the fridge for a month will be more sour than discard sitting for a day or two. Using older discard can alter or deepen the sourdough flavor. If you don't want much sourdough flavor and are making this recipe to use up discard, use a "newer" or less-sour discard. If you want to taste the sourdough flavor, choose a discard that has been in your refrigerator for awhile.