Gently fry oxtail in a pan until golden brown and remove from the pan. Then put all the veg and seeds into the pan with 150g of butter and cook until slightly coloured. Put oxtail back into the pan with veg and cover with 2l of chicken stock. Transfer into oven and cook over night at 85°C.
During that time prepare lyonnaise onions. Gently cook thinly sliced onions, 100g of butter and thyme together until slightly coloured then add about 50ml of chicken stock at a time until evaporated until used 500ml of stock you had left. Onions should be nicely soft and brown in colour.
Next day when cooked pick the meat.
Slice potatoes on a mandoline very thinly. Grease your oven pan or a tray. Layer slices of potataoes slightly overlapping each over, do this 3 times, then add half of oxtail meat, then 3 layers of potatoes, then a layer of lyonnaise onions. Do this process until you have 2 layers of oxtail and 2 layers of onions. Add a little bit of leftover stock to help cook the potatoes and cook in the oven for about an hour at 170°C or until soft.