If you wash and dry them carefully, then slice the oranges 3 or 4mm thick.
Depending on how many you're making up at a time then the ratio is one mugfull of water to two of sugar.
That makes a heavy syrup, you can dilute it down quite effectively, but if you have a lot of orange juice from the fruit then you'll have extra liquid anyway.
Heat the water and sugar in a pan and stir until the sugar is dissolved. Now add the orange slices and the juice, and simmer it as low as you can for twenty minutes or so. Turn off the heat and let the pot poach until cool enough to handle without burning yourself on hot syrup.
Spoon into jars in layers, top up with syrup and screw the lid on tight. Set aside to cool.
These slices are brilliant in cakes, or biscuits, or on top of chicken roasting apparently.
They're good for teas, cocktails, Summer fruit or Winter gluhwein type drinks.
The syrup is great drizzled over pancakes, waffles, or added to a hot toddy.
The fruit in syrup will keep well for years like this. I put the opened jar into the fridge, but it doesn't really need to be chilled. Mine gets most used up in baking or in tea.
If you make up a very heavy syrup and once the slices have poached and cooled, they can be lifted out onto a rack and drained, and then left to dry. They'll crystallise and make crystallised orange slices.
I struggle to get them dry enough here, and to keep them dry, it's easier to make them in syrup.
The other thing that's rather nice with them is to pare them very, very finely and cover the skins in vodka. Set that aside for a few weeks, then strain. Add sugar to taste. Make a cointreau type liqueur, but it honestly depends a lot on the oranges.
M