Preheat the oven to 180 degrees, Gas Mark 4.
In a large bowl, whisk together the egg, milk and olive oil.
Mix in the flour, baking powder and sugar to make a batter.
Grease half of a muffin tin with butter (dairy free if needed). The batter will make six doughnuts.
Pour in the batter, filling the muffin indentation three-quarters of the way, or until all of the mixture is used up.
Place in the oven for 8 minutes.
Remove from the oven and using a spatula, turn the doughnuts over to prevent them forming a muffin shape, and giving them an even bake on each side. Return to the oven for two minutes (check regularly).
Once the doughnuts are golden brown, remove from the oven and leave to cool on a wire rack.
While the doughnuts cool, prepare your piping bag (use a slightly larger nozzle to make sure they are oozing with jam), and add the seedless jam.
Using a metal skewer or cake tester, make a small hole in the side of the doughnut and wiggle inside to make room for the jam. If you don't do this, the jam may cause cracks to form in the doughnut.
Insert the piping back into the hole and fill with as much jam as you can.
Dip your doughnuts into caster, granulated or icing sugar (whichever you prefer) and serve (If the sugar does not stick to the doughnut, you may need to dip it into a little melted butter first).