Preheat an oven to 350°F (175C/155C Fan) and prepare donut trays.
In a large mixing bowl, cream together the sugar and butter. Add the egg and vanilla, beating until smooth.
Next, sift in half of the dry ingredients (flour, baking powder, baking soda, salt and cocoa powder). Beat until just combined.
In a small bowl, mix together the water and instant coffee granules until dissolved. Add this to the donut batter, followed by the yoghurt. Beating to combine.
Sift in the last half of the dry ingredients, beating to combine.
Fold in two ounces of the chocolate chips (this step is optional and you can leave these out if preferred).
Add the batter to a piping bag and fill the donut moulds evenly. This is enough for 12 baked donuts.
Place in the centre of the preheated oven for about 20 minutes - checking for a toothpick inserted in the centre to come out clean.
Remove from the oven - and allow to cool in the pan for a couple of minutes before carefully turning out or unmoulding and allowing to cool on a wire rack.
Once cool, make the ganache by heating the cream in a small saucepan until simmering. Allow to simmer for about 2 minutes. Then, pour over the remaining chocolate chips in a heatproof bowl. Allow to sit for 2 minutes and then stir until smooth.
Dunk or frost each donut generously with the fresh ganache. Top with sprinkles or other decoration if desired.