This is not my usual area of competence (i.e. Augusta is the family jam maker) but…
First the fruit needs to soak . I wash 2 lemons, a grapefriut and an orange and remove the peel with a potato peeler. I cut the peel into fine strips and add it to a bowl with 2 litres of water. I remove the white pith from the fruit and put it in a muslin cloth (actually, an old cotton napkin). I cut up the fruit and put any pips or pith in the the napkin. I add the fruit to the basin of water. I tie up the napkin well and add it to the basin too. I cover with a plate and leave for 24 hours.
I bring the fruit, water and bag of pith to the boil in a very large pan and simmer for an hour and a half. I wash five jam jars and their caps well, dry them and put them in the oven at 100°C for half an hour to “sterilise”. I remove the bag of pith from the simmered liquid and squeeze out as much of the sticky liquid as possible into the pan (this is where the pectin is!). I add a kilo and a half of sugar to the fruit and boil rapidly for 20 minutes until setting point is reached. A little liquid on a cold plate will gel. I transfer the marmalade to a pouring jug and fill the jars to the brim. The caps must be put on immediately.
So, breakfast is now sorted for a wee while.