1. 1. Prepare Your Baking 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 lifting later. This prevents sticking and ensures a clean release.

2. 2. Combine Dry Ingredients: In a large bowl, whisk together the all-purpose flour, granulated sugar, unsweetened cocoa powder, baking soda, and salt. Make sure there are no lumps in the cocoa powder, as this will ensure an even color and flavor throughout the cake.

3. 3. Mix Wet Ingredients: In a separate medium bowl, whisk together the active sourdough starter, buttermilk, vegetable oil, large egg, and vanilla extract until well combined. The mixture should look smooth and slightly creamy.

4. 4. Add Red Food Coloring: Stir the red food coloring into the wet ingredients until the color is evenly distributed and vibrant. This is where your cake gets its signature red hue, so don’t be shy!

5. 5. Combine Wet and Dry Mixtures: Pour the wet red mixture into the bowl with the dry ingredients. Stir gently with a spatula or wooden spoon until just combined. Be careful not to overmix, as this can lead to a tough cake. A few small lumps are perfectly fine.

6. 6. Pour into Pan and Bake: Pour the batter evenly into your prepared 8×8 inch baking pan. Spread it out gently to the corners. Bake for 25-30 minutes, or until a wooden skewer or toothpick inserted into the center comes out clean. The top should spring back lightly when touched.

7. 7. Cool the Cake: Once baked, remove the cake from the oven and let it cool in the pan on a wire rack for about 10-15 minutes. This allows the cake to set before you attempt to remove it.

8. 8. Prepare and Frost: While the cake cools, prepare your cream cheese frosting. Once the cake is mostly cool, carefully lift it out of the pan using the parchment paper overhang, if used, and transfer it to the wire rack to cool completely before spreading the frosting evenly over the top. Slice and serve!