1. 1. Prepare Your Oven and Pan: 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, leaving an overhang on two sides for easy removal. This ensures your cake won’t stick and makes cleanup a breeze.

2. 2. Combine Dry Ingredients: In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, ground cinnamon, and salt. Make sure there are no lumps and the spices are evenly distributed. This step is crucial for an even rise and flavor.

3. 3. Cream Wet Ingredients: In a large bowl, using an electric mixer or a whisk, cream together the softened unsalted butter and granulated sugar until the mixture is light and fluffy. This usually takes about 2-3 minutes. Scrape down the sides of the bowl as needed.

4. 4. Incorporate Egg and Sourdough Discard: Beat in the large egg until well combined, then stir in the sourdough discard and vanilla extract. Mix until just incorporated; overmixing at this stage can lead to a tough cake. The mixture might look slightly curdled, but don’t worry, it will come together.

5. 5. Combine Wet and Dry Mixtures: Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed or by hand until just combined. Be careful not to overmix; a few streaks of flour are fine. Overmixing develops gluten, which can make the cake dense.

6. 6. Fold in Peaches: Gently fold in the diced peaches. Distribute them evenly throughout the batter. If using fresh peaches, ensure they are ripe but firm. If using canned, make sure they are very well-drained to avoid adding excess moisture to the batter.

7. 7. Bake the Cake: 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 crunchy crust. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean. The cake should be golden brown and spring back when lightly touched.

8. 8. Cool and Serve: Let the cake cool in the pan on a wire rack for at least 15-20 minutes before attempting to remove it. This allows the cake to firm up. Once slightly cooled, you can lift it out using the parchment paper overhangs or invert it onto a wire rack to cool completely before slicing and serving.