Description

Looking for a delicious way to use your sourdough discard and fresh rhubarb? Moist Rhubarb Sourdough Discard Cake is a tender, tangy-sweet dessert that combines the tartness of rhubarb with a soft, lemony cake, all enhanced by the subtle tang of sourdough discard.

Ingredients

This Rhubarb Sourdough Discard Cake uses pantry staples and fresh rhubarb for a flavorful, moist cake. Here’s what you need and why each one matters:

Fresh Rhubarb (8 ounces, ~2 cups): Provides tart flavor and visual appeal; ¾ cut into ½-inch chunks for the batter, the rest into longer pieces for a decorative top pattern.
All-Purpose Flour (170 grams, ~1⅓ cups): Forms the cake’s structure; lightly coats rhubarb to prevent sinking.
Baking Powder (1½ teaspoons): Ensures a tender, risen crumb.
Fine Salt (½ teaspoon): Balances sweetness and enhances flavors.
Cane Sugar (155 grams, ~¾ cup, divided): Sweetens the cake (145 grams in batter, 10 grams for topping) and adds a slight crunch on top.
Sunflower or Grapeseed Oil (½ cup): Keeps the cake moist and tender, with a neutral flavor.
Lemon Zest (2 teaspoons): Adds bright, citrusy aroma to complement rhubarb.
Eggs (2, room temperature): Bind the batter and add richness; room temperature ensures even mixing.
Runny Honey (2½ tablespoons): Adds natural sweetness and moisture with a subtle floral note.
Sourdough Discard (65 grams, ~¼ cup, preferably room temperature): Contributes slight tang and moisture, reducing waste.
Vanilla Extract (1½ teaspoons): Enhances flavor with warm, sweet notes.
Fresh Lemon Juice (1 tablespoon): Boosts tartness and balances sweetness.
Whole Milk (2½ tablespoons): Adds moisture and tenderness to the crumb.

Substitutions and Variations

Rhubarb: Use frozen rhubarb (thawed, drained, and patted dry); substitute ½ cup chopped strawberries or raspberries for part of the rhubarb (adjust sugar down by 1 tablespoon).
Flour: Swap for gluten-free 1:1 baking flour for a gluten-free version; ensure proper weight (170 grams).
Baking Powder: Ensure fresh for proper rise; no substitute without altering texture.
Cane Sugar: Use granulated sugar or coconut sugar (may darken flavor); reduce topping sugar for less crunch.
Oil: Replace with melted butter or avocado oil; butter adds richer flavor but may firm up when cold.
Lemon Zest/Juice: Swap for orange zest/juice or omit zest (use ½ teaspoon more vanilla for flavor).
Eggs: Use flax eggs (2 tablespoons ground flaxseed + 5 tablespoons water, let sit 5 minutes) for vegan, but texture may be denser.
Honey: Substitute with maple syrup or agave nectar; honey adds unique flavor.
Sourdough Discard: Use active sourdough starter (same amount) or increase flour by 30 grams and milk by 2 tablespoons if no discard (lose tangy flavor).
Vanilla Extract: Omit or use ½ teaspoon almond extract for a twist.
Milk: Swap for plant-based milk (e.g., almond, oat) for dairy-free; whole milk adds richness.
Add-Ins: Mix in ¼ cup chopped walnuts or ½ teaspoon cinnamon to the batter for extra texture or warmth.

Pro Tip: Weigh ingredients (e.g., 170 grams flour, 65 grams discard) for accuracy, as volume can vary. Use room-temperature eggs and discard for a smoother batter; trim rhubarb’s woody ends for best texture.

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Instructions

Prepare the Oven and Pan:
- Preheat oven to 350°F (177°C).
- Grease an 8-inch or 9-inch square cake pan and line with parchment paper, leaving overhang for easy removal.
- Tip: Ensure parchment covers the bottom and sides; grease lightly under and over parchment for extra insurance.
Prep the Rhubarb:
- Trim and cut 8 ounces rhubarb: ¾ (6 ounces, ~1½ cups) into ½-inch chunks, the rest into longer pieces (2-3 inches) to fit diagonally across the pan for decoration.
- Place chunks in a medium bowl.
- Tip: Cut rhubarb uniformly for even baking; save prettiest pieces for the top pattern.
Mix Dry Ingredients:
- In another medium bowl, whisk 170 grams all-purpose flour, 1½ teaspoons baking powder, and ½ teaspoon fine salt.
- Scoop 2 heaping teaspoons of this mixture into the bowl with the rhubarb chunks and toss to coat (prevents sinking in batter). Set both bowls aside.
- Tip: Toss rhubarb gently; a light flour coating is enough.
Make the Batter:
- In a stand mixer (or large bowl with a hand mixer), beat 145 grams cane sugar, ½ cup sunflower or grapeseed oil, and 2 teaspoons lemon zest on medium speed for 1 minute until slightly frothy and sugar begins to dissolve.
- Add 2 room-temperature eggs and beat on medium for 30 seconds until frothy and well combined.
- Add 2½ tablespoons runny honey, 65 grams sourdough discard, 1½ teaspoons vanilla extract, 1 tablespoon fresh lemon juice, and 2½ tablespoons whole milk. Mix on medium speed until just combined, about 15 seconds.
- On low speed, gradually add the dry flour mixture, mixing just until no flour streaks remain (do not overmix).
- Tip: Scrape the bowl as needed; stop mixing once flour is incorporated to keep the cake tender.
Fold in Rhubarb:
- Gently fold the flour-coated rhubarb chunks into the batter using a spatula. It’s okay if some flour is visible on the rhubarb.
- Tip: Fold carefully to avoid crushing rhubarb; ensure even distribution.
Assemble the Cake:
- Pour the batter into the prepared pan and smooth the top with a spatula.
- Arrange the longer rhubarb pieces on top in a decorative pattern (e.g., diagonal lines or a lattice).
- Sprinkle the top evenly with the remaining 10 grams (2 heaping teaspoons) cane sugar for a crunchy finish.
- Tip: Press rhubarb pieces lightly into the batter; sugar adds sparkle and texture.
Bake the Cake:
- For an 8-inch pan: Bake at 350°F for 25 minutes, then reduce oven to 330°F (166°C) and bake 15 minutes more, until a toothpick inserted in the center comes out with a few moist (not wet) crumbs.
- For a 9-inch pan: Bake at 350°F for 20 minutes, then reduce to 330°F and bake 8-10 minutes more, until a toothpick tests similarly.
- Tip: Check doneness early to avoid overbaking; tent with foil if the top browns too quickly.
Cool and Serve:
- Remove the cake from the oven and cool in the pan on a cooling rack for 30 minutes.
- Lift the cake out using the parchment overhang, slice, and serve warm or at room temperature (makes 9-12 servings).
- Store in a sealed container in the refrigerator for up to 4 days.
- Tip: Let cool slightly for cleaner slices; serve with whipped cream or yogurt for extra indulgence.

Cooking Tips:

Prevent Overbaking: Check with a toothpick early; moist crumbs indicate doneness, while a wet batter needs more time.
Rhubarb Placement: Arrange top rhubarb pieces thoughtfully for a pretty presentation; avoid overlapping too much.
Mix Gently: Overmixing the batter can make the cake dense; fold rhubarb with care to maintain tenderness.