Put the yoghurt in a bowl and mix in all the zest.
Take a glass serving dish and put just under half the citrus yoghurt in the bottom, then evenly scatter over half the sugar. (Muscovado tends to get little hard lumps in it, so really try to crumble them out between your thumb and finger.)
Add the rest of the yoghurt in dollops over the sugar and them gently spread it out with the back of a spoon so as not to drag the first layer of sugar around too much.
Scatter the rest of the sugar on the top and place the puddin, covered, in the fridge for up to a couple of hours but no more.
Serve alone, or with biscuits, or poached fruit - or both, God damn it!
