Using a sharp knife, cut a line lengthwise across (and through to the meat of the nut) the curved outer part of the shell.
Place in a foil boat on a baking sheet and sprinkle with shallots and orange zest. Add the brandy and orange juice.
Wrap up the top and roast for about 20 minutes, until the skins have peeled back from the chestnuts. **If the skins have not started to peel back, roast longer
Remove and place the foil packet in a towel and wrap tightly for about 10 minutes.
Dump the chestnuts in a bowl and toss with the salt and melted butter (optional).
Peel back the skin (and the thin brown layer underneath if it doesn't come off with the skin) and pop the chestnuts out to enjoy!
Notes
Chestnuts should be stored in the fridge for up to 3 days before using (they spoil quickly).
Make sure to cut all the way down to the flesh of the chestnut when scoring to make sure the steam can escape.
If the skins haven't started to peel back after 20 minutes, continue roasting until they have.
Cover them with a towel after removing from the oven to make sure they steam properly.
Tossing in butter and salt is optional - I find it adds an extra oomph, but feel free just to peel and eat plain.
You can also toss them in butter and salt once peeled.
Chestnuts are best when eaten immediately (still warm).