In a large bowl, combine 3 1/2 cups of all purpose flour, 2 teaspoons of salt, 1/2 teaspoon of instant yeast, 1 tablespoon of espresso powder and 2 tablespoons of granulated sugar
Add 1/2 cups of room temperature water and mix until a sticky dough develops and no dry flour in left unincorporated
Cover the bowl tightly with plastic wrap and let it rest at room temperature for 8-12 hours
An hour before baking, place your dutch oven with lid or a bread cloche into a cold oven and preheat to 450 degrees
While the oven and vessel are preheating, transfer your dough onto a lightly floured surface
Gently work the dough out into a square-ish shape and sprinkle about half of the chopped chocolate and walnuts over the surface
Fold the dough in thirds bring the top third toward you and then folding the bottom third over the top, so the dough is folded like a letter
Gently press the dough out a bit and add the remaining chopped chocolate and walnuts and then roll the dough into a spiral and tuck under the edges to shape the loaf into a round ball
Place the shaped loaf onto a sheet of parchment paper and cover with a clean kitchen towel
When the oven has been on for an hour, carefully transfer the preheated vessel onto a heat proof surface and remove the lid
Use the corners of the parchment to carefully transfer the dough into the vessel
Optional: use a bread lame or sharp knife to make a shallow cut into the top surface of the dough to help the dough expand in a controlled way
Bake the dough covered for 30 minutes
Uncover the vessel and bake the bread for an additional 15 minutes or until the crust is golden brown and crisp and the loaf has an internal temperature of 200 degrees
Carefully transfer the loaf out of the vessel and onto a cooling rack to cool fully before slicing