Mix the sourdough base

• Combine the bread flour, water and sourdough starter in a bowl.
• Mix until no dry flour remains, then cover and rest.

Add salt and divide the dough

• Sprinkle the salt over the dough and work it in until fully absorbed.
• Split the dough in two and blend the cocoa powder into one half until evenly dark.

Laminate the two doughs

• Stack the plain and cocoa doughs and roll them out together.
• Fold and roll a few times to create the marble pattern.

Bulk ferment

• Shape the marbled dough into a ball and place it in a bowl.
• Cover and let it rise until puffy and increased in volume.

Shape and proof

• Shape the dough into a tight round and place it seam-side up in a floured banneton.
• Cover and proof until ready to bake.

Bake the loaf

• Preheat the oven with a covered dutch oven inside.
• Score the loaf, bake covered, then uncovered until deep golden and hollow-sounding.

Whip the chocolate butter

• Beat the softened butter until pale and fluffy.
• Add the melted dark chocolate and powdered sugar and whip until smooth.

Cook the raspberry jam

• Simmer the raspberries, granulated sugar and lemon juice, crushing the fruit.
• Cook until thickened, then cool completely.

Serve

• Slice the cooled marble sourdough.
• Spread with chocolate butter and raspberry jam.