• Wash the oranges, then cut in half and juice. Keep the juice, peel and pips and pith. The easiest way to do this is with an electric juicer, but if you don't have one then a traditional juicer or reamer will also work perfectly well.
• Slice the orange peel into strips. The easiest way to do this is by cutting each half peel into three . Then stack the three strips on top of each other and cut across into narrow strips.
• Measure the fruit juice into the Instant Pot. Make the liquid up to equal the original weight of oranges. I.e., I started with 1kg of oranges, so made the liquid up to 1 litre.
• Add the lemon juice, sliced orange peel, and the pith and juice tied into a muslin cloth.
• Pressure cook the mixture on high pressure for 15 minutes. Release the pressure once cooked and check that the peel is soft and will cut easily with a spoon.
• Remove the bag of pips and squeeze out the juice. One easy way of doing this is by pressing the bag between two plates.
• Add the sugar. It looks like a lot of sugar, but don't worry, it will all dissolve. The very high bitterness of the Seville oranges needs this much sugar to make a tasty marmalade.
• Set the instant pot onto the low sauté setting. Stir the mixture as the sugar dissolves.
• Once the sugar has dissolved, turn the Instant Pot up to the high saute setting, and keep stirring until you have reached the setting point. Check for a set by either using a preserving thermometer, the plate method or the flake method.
  

Testing for setting point. Use one of these three methods.

• The temperature test. Really accurate electronic jam thermometers are readily available, and not expensive. They are much easier to read than traditional thermometers. Heat the marmalade to the 105°C and once it's that hot it should at at setting point.   I always test with a wrinkle test.
  
• The wrinkle test. Place a couple of side plates in the freezer before you add the sugar. Once the marmalade is boiling, start testing by placing some on the plate. Allow it to cool and when you push your finger through the marmalade, if it's setting you'll see it wrinkle up a little ahead of your finger. This technique takes a bit of practice.
• The flake test. Take a spoonful of marmalade from the pan and turn it vertically to tip it out. If the marmalade runs off quickly and completely it hasn't set. If, however a little remains on the spoon in a sort of wide drip that doesn't fall, then the marmalade is ready. Again, this works best with some practice.

Once setting point has been reached

• Let the Instant Pot Seville orange marmalade cool for about 10 minutes, and then transfer to the warmed jam jars. Fit the lids and allow to cool completely.