Ingredients

Leaven:
50g 100% hydration starter
50g Wholemeal Spelt
50g water

Dough:
250g Wholemeal spelt
250g Strong white flour
330ml water
10g salt
~200g Chestnuts (unpeeled)

Method
Make the leaven ~6-10 hours before use (depending on the vigour of your starter and temperature)

Mix the flour and water and leave for ~1hour to autolyse (optional, for stronger, more elastic dough)

Cut crosses on the chestnuts and roast in the oven for about 15 minutes at 165 degrees. Peel of the shells (and as much of the inside skin). Mash the chestnuts to the desired chunk size. Set to cool.

Mix the flour/water mix with the leaven for 5-10 minutes. Mix in the salt. If the dough is too firm, add a bit of water and mix until it is absorbed. Do 3 sets of stretch and folds, spaced half an hour apart. Fold in the chestnuts on the last fold. Leave for another 2 hours after the last fold.
Shape the loaf and place in either a banneton or tin. Leave in a cool place (fridge or cold room in winter) overnight.

Next day, pre-heat the oven to 235 degrees (c. Use a Dutch oven, if possible, for better rise and crust. Score and bake the loaf straight from the fridge (or room) for 40 minutes. If using a Dutch oven, remove the lid after 20 minutes. Keep an eye on the colour near the end and reduce the temperature if necessary.