Let’s bake this unique and moist Rhubarb Sourdough Discard Cake:

1. Preheat Oven and Prepare Pan & Rhubarb:

• Preheat your oven to 350°F (175°C).
• Grease and line an 8-inch square cake pan with parchment paper, leaving an overhang on two sides to act as “handles” for easy removal.
• Prepare your rhubarb: Wash and trim the rhubarb stalks. Cut about ¾ of the rhubarb (6 oz) into ½-inch chunks. Cut the remaining ¼ of the rhubarb (2 oz) into longer, thinner pieces that will fit nicely on top of the cake in a decorative pattern. Place the ½-inch chunks into a medium bowl.

2. Prepare Dry Ingredients & Coat Rhubarb:

• In another medium bowl, whisk together the all-purpose flour, baking powder, and fine sea salt until well combined.
• Scoop 2 heaping teaspoons from this flour mixture and add it to the bowl with the chopped ½-inch rhubarb chunks. Toss the rhubarb gently until it is lightly coated in flour. This clever trick helps prevent the rhubarb from sinking to the bottom of the cake. Set both bowls aside.

3. Mix the Wet Ingredients:

• In the bowl of a stand mixer fitted with the paddle attachment (or in a large bowl using a handheld electric mixer), add 145 grams (most of your measured amount) of the cane sugar, the sunflower or grapeseed oil, and the lemon zest.
• Beat on medium speed for 1 minute. This step helps dissolve the sugar and releases the fragrant oils from the lemon zest.
• Add the room temperature eggs and beat for another 30 seconds on medium speed, until the mixture is pale, frothy, and well combined. Scrape down the sides of the bowl.
• Add the honey, room temperature sourdough discard, vanilla extract, fresh lemon juice, and whole milk to the bowl. Mix on medium speed until these ingredients are just combined.

4. Combine Wet and Dry to Make Batter:

• With the mixer on low speed, gradually add the dry ingredient mixture (from Step 2) to the wet ingredient mixture.
• Mix just until no dry bits of flour remain. Do not overmix! Overmixing will develop gluten and can make the cake tough.

5. Fold in Rhubarb and Assemble:

• Gently fold the flour-coated rhubarb chunks into the prepared batter using a rubber spatula.
• Pour the batter into the prepared 8-inch cake pan and use the spatula to smooth the top into an even layer.
• Arrange the longer, decorative pieces of rhubarb on top of the batter in any pattern you’d like.
• Sprinkle the top of the cake evenly with the remaining 10 grams (about 2 heaping teaspoons) of cane sugar.

6. Bake the Cake (Two-Temperature Method):

• Place the cake pan in the preheated 350°F (175°C) oven.
• Bake for 25 minutes.
• After 25 minutes, turn the oven down to 330°F (165°C).
• Continue to bake for about 15 minutes more. The cake is done when a toothpick inserted into the center comes out with a few moist (but not wet) crumbs attached. For a 9-inch cake pan, adjust times as noted in the original recipe (20 mins at 350°F, then 8-10 mins at 330°F). Be careful not to overbake.

7. Cool and Serve:

• Remove the cake from the oven and let it cool completely on a wire rack in the pan.
• Once completely cool, use the parchment paper overhang to lift the cake out of the pan.
• Slice and serve. In a sealed container, this cake stores very well in the refrigerator for up to 4 days.

The two-temperature bake helps the cake set and cook through evenly without over-browning.