Turn on the sauté function on the pressure cooker and add 1 tbsp of oil, allow it to heat for a few minutes.
Add the diced pork to brown it, for 3–4 minutes. This adds extra flavour but is optional if you’re short on time.
Remove the pork from the pot and set to one side.
Add the onions and garlic to the pot. Cook for 2–3 minutes until softened. If there are any bits stuck to the base of the pot use a wooden or silicone spoon to deglaze it, make sure that nothing is stuck on to the base of the pot. Add a little of the hot stock if necessary to help remove it.
Turn off the sauté function. and return the pork to the pot and add the chopped carrots, leeks, mustard, chopped tomatoes, tomato purée, mixed herbs, bay leaves, and vegetable stock.
Stir everything well to combine.
Close the lid and set the valve to "Sealing."
Use the pressure cook or manual setting and cook on high pressure for 25 minutes.
Once cooking time is complete, allow the pressure to release naturally for 10 minutes, then carefully perform a quick release.
If you prefer a thicker sauce, turn on the sauté function after cooking and leave to simmer until it thickens up.
Or, alternatively, stir in a slurry of 1 tbsp cornflour mixed with 2 tbsp water, and simmer for 2–3 minutes until thickened to your liking. Or, stir in some of your favourite gravy granules to thicken it.
Remove the bay leaves before serving.
Serve the casserole with mashed potatoes, rice, or crusty bread.