- Step 1: Prepare the Oven and Pan: Preheat the oven to 350F (175C). Grease and flour a 9x13 inch baking pan. This ensures the cake releases easily after baking. Alternatively, use baking spray with flour. 
- Step 2: Combine Wet Ingredients: In a large mixing bowl, whisk together the vegetable oil, milk, eggs, and vanilla extract until well combined. This forms the base of the cake batter, ensuring a consistent texture. 
- Step 3: Incorporate Dry Ingredients: Add the yellow cake mix to the wet ingredients. Gently mix until just combined. Be careful not to overmix, as this can result in a tough cake. A few lumps are okay. 
- Step 4: Add the Peaches: Fold in the diced peaches and cinnamon (if using) into the batter. Ensure the peaches are evenly distributed throughout the mix for consistent flavor in every slice. 
- Step 5: Pour and Prepare for Baking: Pour the batter into the prepared baking pan, spreading it evenly. If desired, sprinkle the top with granulated sugar and drizzle with melted butter for added flavor and a golden-brown crust. 
- Step 6: Bake to Perfection: Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Begin checking for doneness at 30 minutes to prevent overbaking. 
- Step 7: Cool and Serve: Let the cake cool in the pan for 10-15 minutes before slicing and serving. Cooling slightly allows the cake to firm up, making it easier to slice. 
- Optional Tips: 
- - For a richer flavor, substitute melted butter for the vegetable oil. 
- - Add a streusel topping made with flour, butter, and sugar for extra texture and sweetness. 
- - Consider using a white cake mix instead of yellow for a lighter color and flavor profile. 
- - If fresh peaches aren't available, use frozen peaches (thawed and drained) or canned peach pie filling (reduce milk by 1/4 cup).