1. Preheat your oven to 350 F (175 C). Lightly grease and flour an 8×8-inch baking pan, or line it with parchment paper, leaving an overhang on the sides for easy lifting later. This prevents sticking and ensures a clean release.

2. 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 the ingredients are evenly distributed. This ensures consistent leavening throughout the cake.

3. In a separate medium bowl, whisk together the sourdough discard, milk, melted butter, egg, and vanilla extract until well combined and smooth. The melted butter should be cooled slightly so it doesn’t scramble the egg.

4. Pour the wet ingredients into the dry ingredients. Mix with a spoon or spatula until just combined. Be careful not to overmix; a few small lumps are perfectly fine. Overmixing can lead to a tough cake.

5. Gently fold in the diced peaches. Distribute them evenly throughout the batter. If using fresh peaches, ensure they are peeled and diced into small, bite-sized pieces. If using canned, drain them thoroughly to avoid excess moisture.

6. Pour the batter into your prepared 8×8-inch baking pan and spread it evenly. If desired, sprinkle the top with turbinado sugar for a lovely crunch and sparkle.

7. Bake for 25-30 minutes, or until a wooden skewer or toothpick inserted into the center of the cake comes out clean. The top should be golden brown and the edges slightly pulled away from the pan.

8. Let the cake cool in the pan on a wire rack for at least 10-15 minutes before slicing and serving. This allows the cake to set and makes it easier to cut.