Add a splash of oil to a wide saucepan and set over a medium heat.

When hot, add the onion and garlic and gently sweat for 10 minutes, until translucent and soft, but without colour.

Stir in the remaining vegetables and cook for a further 5 minutes. Increase the heat, pour in the wine and reduce by half. Stir in the thyme and tomato purée and cook for 1-2 minutes before mixing in the flour a little at a time.

Pour the stock into the pan, mixing thoroughly with each addition until you have a nice thick, smooth sauce.Remove from the heat, stir through the gammon pieces and check the seasoning.

Set aside until needed.

To make the bubble and squeak topping, set a frying pan over a medium heat and add a splash of oil.Gently fry the onion in the oil until soft and translucent, then remove from the heat and set aside to cool completely.

Mash the potato and greens together in a bowl using a fork (or pulse a few times in a food processor if you have one) until the two are well combined, then stir in the cold cooked onion.

Pour the gammon filling into a baking dish and evenly spread the bubble and squeak mash on top.

Use a fork to decorate the top of the mash, drizzle over a little olive oil and bake in the oven for 30 minutes, until the top is golden and crispy.