Tip the dough out of the bowl onto the counter so the sticky side is ontop. If you're making one large stollen, then leave the dough as is, but if you would prefer two smaller stollens, divide the dough into two equally weighted pieces.
Gently pull each piece of dough out into a rough rectangle. Mold the marzipan into two long cylinders, the same length as your dough and lay off centre on the long side of each piece dough.
Spinkle the dough with cinnamon and nutmeg if desired.
Roll each rectangle of dough into a long roll (similar to when you make sourdough cinnamon rolls). Start on the side where you've laid the marzipan and roll, tucking the bottom seam under, along with the ends. You want to completely conceal the marzipan so that it doesn't leak out in the oven.
Transfer each stollen to a baking tray lined with baking paper and cover with a damp kitchen towel. Allow the stollen to proof at room temperature until the dough has risen around 50% again.
When you're ready to bake the stollen, preheat the oven to 175C (350F).
When the oven is at temperature, bake the sourdough stollen for around 45 minutes (or until it is golden brown).
Remove the baked sourdough stollen from the oven and allow to cool for a bit before brushing it all over with melted butter (a pastry brush is perfect for this).
Once it's cooled for around an hour, brush it again with butter and then place into a container full of powdered sugar. Lightly roll the stollen around in the powdered sugar until it's completely and evenly covered on all surfaces.
Now, wrap your stollens in a piece of aluminum foil and allow them to mature for at least 24 hours before you try them (it's worth the wait I promise).