Pour the warm milk into a jar and stir in the yeast and 1/2 teaspoon of caster sugar. Leave for a few minutes until frothy.
In a large bowl whisk together the flour and salt. Mix together the caster sugar and lemon zest and add it to the bowl. Stir until well combined and then create a well in the centre, pour in the frothy mixture followed by the melted butter and egg. Stir until well combined.
Tip dough out onto a floured work surface and knead for 5 minutes. Flour hands and surface as needed. The dough is meant to be sticky so try not to add too much extra flour.
Place dough back into the bowl and cover with cling film. Leave in a warm place until doubled in size (around 1 to 1 1/2 hours).
Once risen, punch down the dough and knead for a few minutes. Using a rolling pin, roll out dough to 1/2 inch thick and use a floured cookie cutter to cut out the doughnuts.
Taking a smaller cookie cutter, cut holes out of the centre of each doughnut. Use the excess dough to make more doughnut holes. Arrange the ring doughnuts and doughnut holes onto a floured tray, cover with clingfilm and leave to double in size a second time (around 20-30 minutes).
Once risen fry the ring doughnuts in vegetable oil at 180°C, 2 or 3 at a time, for 2-3 minutes. Make sure to rotate a few times. Place the cooked doughnuts on a sheet of kitchen roll to drain off excess oil. The doughnut holes will only take 1 minute to fry.
Once cool enough to handle, roll the doughnut holes in caster sugar mixed with lemon zest before filling with cherry jam.
For the cherry glaze, blitz together pitted cherries with the lemon juice and icing sugar. Sieve to remove any cherry skin.
In a bowl stir together the melted butter with the sifted icing sugar until combined. Stir in sieved cherry mixture a little at a time until you have reached your desired consistency.
Dip the top of the ring doughnuts into the glaze and leave to set. Enjoy :D