Make sponge: Mix sourdough discard, water, and flour together into a thick sponge. Cover well and let sit at room temperature 6 to 10 hours or overnight.
Preheat: Preheat oven to 350º
Grate zucchini: Grate zucchini into coarse pieces using a clean cheese grater. Place zucchini in a fine mesh strainer propped over a bowl to allow excess water to drain.
Beat butter: Place a large mixing bowl on the scale. Tare the bowl then add butter. Cream butter. Add oil and brown sugar. Beat together until creamy.
Scale: Add eggs, vanilla, and salt. (Remember to use the scale’s tare function to remove the weight of the bowl and previous ingredients to only weigh the current item added)
Mix: Beat ingredients together.
Add sponge: Use a spatula to add your sponge and mix well until all the ingredients are incorporated..
Mix spices and baking soda: In a separate bowl, mix baking soda and spices. Pour dry mixture into the wet mixture. Stir together.
Add zucchini: Once combined, add the grated and drained zucchini.
Prepare muffin pan: Place liners into the cups of the muffin pan.
Fill muffin cups: Use a spatula to pour dough into the cups, equally distributed and about ¾ full. For an extra crispiness on top, sprinkle ½ to 1 teaspoons sugar over the top of each muffin before baking.
Bake: Place pans into oven and bake 18 to 22 The tops should be golden brown and a toothpick or knife inserted into the center should come out clean.
Cool: Allow to cool for about 10 to 15 minutes.