Prepare the collected chestnuts:

If you have bought packaged chestnuts, you can skip this step.
Boil the fresh chestnuts in a saucepan until they are soft (mine took 30 minutes).
Drain the water, leave the chestnuts to cool, then take each one in turn, cut them in half and scrap the nuts out with a teaspoon.

Cook the chestnut spread:

If you have bought pre-cooked chestnuts, cut them into rough pieces.
Pit and chop the dates.
Slit the vanilla pod open lengthwise, and scrape out the vanilla pulp.
Place the chestnuts, empty vanilla pod, vanilla pulp and dates in a pan, add oat milk and rapeseed oil and cook over a low heat for 15 minutes.
Remove the vanilla pod from the cooked mixture.
Blend everything with a hand blender until it is creamy.