If cooking in the oven rather than an Instant Pot: preheat the oven to 160 C /140 C Fan / Gas 4 and put a large, lidded casserole dish inside to heat up.

Put the olive oil in a large frying pan on a high heat.

Lightly season the oxtail pieces with salt and pepper.

Brown the oxtail all over in the oil. Do this in batches if necessary.

If using an Instant Pot (IP)

Transfer the browned oxtail to the IP inner, placing in one layer if possible.

Add the rest of the broth ingredients, plus a pinch of salt then lock on the lid.

Ensure the valve is set to 'Sealing' then press the 'Manual' button. Use the +/- buttons to set the time to 60 minutes.

When the time is up, leave for 10 minutes, press 'Keep Warm/Cancel', then release the pressure manually (or leave pressure to release naturally if preferred).

If cooking in the oven

Transfer the browned oxtail to a lidded casserole dish, placing in one layer if possible.

Add the rest of the broth ingredients, plus a pinch of salt.

Put on the lid, bring to a boil on top of the stove then transfer to the oven.

Cook until the oxtail is very soft and almost falling from the bone (3 - 4 hours).

Using a slotted spoon, transfer the pieces of oxtail from the broth to a bowl. Set aside to cool a little.

Pour the broth through a sieve into a large heatproof bowl. Discard the contents of the sieve and leave the broth to cool. Cover and store in the fridge when cold.

As soon as the oxtail is cool enough to handle, separate the meat and discard any fat and sinew: this is easiest to do while it's still warm.

Shred or dice the meat and put it in a covered container in the fridge.

Put the butter in a large saucepan over low heat.

Stir in the onions and garlic plus a little salt and pepper.

Put on a lid and sweat very slowly until soft but not colouring, stirring occasionally (40-45 minutes).

While the onions are cooking: take the stock from the fridge and skim off any unwanted fat (this can be stored in a jar in the fridge and kept for cooking potatoes or other dishes).

Measure out 1 litre of stock (any extra will keep in the fridge for 2 days or can be frozen).

Turn the heat up to medium and, stirring often, cook to evaporate off any water and further soften the onions: after 10 minutes they should be lightly golden.

Pour in the port, turn the heat to high and bubble until the port is almost completely evaporated (2-3 min).

Tip: if you want a thicker soup, stir in 1 level tbsp flour now.

Add the bunch of thyme, the litre of oxtail stock and season with a little salt and a generous amount of pepper.

Put on the lid, bring to a boil then immediately turn down to a low simmer for 10 minutes.

Stir in the reserved oxtail meat and simmer for a further 10 minutes.

Tip: if you want to reduce the broth then simmer with the lid off. Otherwise leave the lid on.

Remove the bunch of thyme then taste and add more seasoning if needed.

Take off the heat.

The soup can be chilled and stored in the fridge or frozen at this stage.

Preheat the oven to 170 C / 150 C Fan / Gas 3.

Put the slices of bread on a tray in the oven and bake for 10 minutes or until dryish, turning halfway through. (Alternatively, lightly toast the bread).

Heat your grill to high.

Divide the soup between six small-medium heatproof bowls* so it almost reaches the top.

Place a slice of bread on each soup and scatter with the grated cheese.

Put the bowls under the grill and cook until the cheese is melted and bubbling.

* If you don't have heatproof bowls then put the slices of bread, scattered with cheese, on a tray under the grill until bubbling. Put a slice on each bowl of soup.

Serve immediately.