1. Prepare Your Baking Pan and Oven: Preheat your oven to 350 F (175 C). Lightly grease and flour an 8×8 inch square baking pan or line it with parchment paper for easy removal. This prevents sticking and ensures a clean release.

2. Combine Dry Ingredients: In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and salt. Make sure there are no lumps and everything is evenly distributed.

3. Mix Wet Ingredients: In a separate medium bowl, whisk together the sourdough discard, melted butter, milk, egg, orange zest, and fresh orange juice until well combined. The mixture should be smooth and slightly frothy.

4. Combine Wet and Dry Mixtures: Pour the wet ingredients into the dry ingredients. Stir gently with a spatula or wooden spoon until just combined. Be careful not to overmix; a few small lumps are perfectly fine and will result in a tender cake. Overmixing can lead to a tough texture.

5. Pour into Pan and Bake: Pour the batter evenly into your prepared baking pan. Spread it out gently with the back of a spoon or spatula.

6. Bake Until Golden: Bake for 20-25 minutes, or until a wooden skewer or toothpick inserted into the center of the cake comes out clean. The top should be lightly golden brown and spring back when gently pressed.

7. Cool and Glaze (Optional): Let the cake cool in the pan on a wire rack for about 10-15 minutes before carefully transferring it to the wire rack to cool completely. While it cools, whisk together the powdered sugar and orange juice for the glaze. Drizzle the glaze over the cooled cake before slicing and serving.