1. 1. Prepare your sourdough loaf: Using a sharp serrated knife, slice your unsliced sourdough bread horizontally into 1-inch thick slices, but do not cut all the way through the bottom crust. You want the slices to remain connected at the base, creating an accordion-like effect. Then, make a second set of cuts vertically across the first cuts, again not cutting through the bottom crust, creating a grid pattern. This allows the chocolate mixture to seep into every crevice.

2. 2. Create the chocolate filling: In a medium bowl, combine the softened unsalted butter, granulated sugar, unsweetened cocoa powder, vanilla extract, and a pinch of salt. Use a fork or a small whisk to mix until the mixture is smooth and well combined. It should have a thick, spreadable consistency.

3. 3. Add the milk for consistency: Stir in the tablespoon of milk. This will help loosen the chocolate mixture slightly, making it easier to spread and ensuring it melts beautifully into the bread. If adding chocolate chips, fold them in now.

4. 4. Fill the sourdough bread: Gently open up the cuts in your sourdough loaf. Using a small spoon or a butter knife, carefully spread the chocolate mixture into all the cracks and crevices of the bread. Don’t be shy – make sure each slice gets a good coating of the chocolate goodness.

5. 5. Prepare for baking: Preheat your oven to 350 F (175 C). Place the filled sourdough loaf on a baking sheet lined with parchment paper or foil for easy cleanup. You can also lightly tent it with foil if you’re worried about the top browning too quickly.

6. 6. Bake to perfection: Bake for 20-25 minutes, or until the chocolate filling is melted and bubbly, and the bread is warmed through and slightly crisp on the outside. The aroma filling your kitchen will be your cue that it’s almost ready!

7. 7. Serve warm: Carefully remove the bread from the oven. Let it cool for a few minutes on the baking sheet before transferring it to a cutting board. The individual pieces can be easily pulled apart for serving.