Trim the bottom off each brussel sprout then remove any loose, outer leaves.
Thinly slice the sprouts either with a sharp knife or with a food processor & a slicing attachment then set aside.
Roughly chop the chestnuts then set aside for later.
Next, place a large saucepan over a medium heat & pour in the tablespoon of veg oil.
Once the oil's hot, add in the bacon & cook until crispy, stirring frequently. This will take around 5 minutes.
Remove the cooked bacon from the pan & transfer to a bowl.Leave the bacon fat in the pan! Next, add the sprouts & butter into the pan, season with salt and pepper then cook for 2-3 minutes, until the sprouts have started to soften.
Pour in the double cream & chicken stock then bring to a simmer.
Cook, stirring occasionally until the sauce has reduced by half then add in the crispy bacon & roughly chopped chestnuts. The cream will take roughly 4-5 minutes to reduce. Cook for another 2 minutes then remove the pan from the heat.
Grate in ⅔ of the parmesan then stir to melt. Taste the sprouts, to check the seasoning (adding more if necessary) then spoon the sprouts into a dish.
Grate the remaining parmesan over the top then serve immediately.