Pour a 6–8cm (2½–3½ inch) depth of vegetable oil into a wide saucepan and place over a medium–high heat until it reaches 180°C/350°F.
Put the ricotta into a food mixer or bowl and add the eggs, caster sugar, flour, baking powder and vanilla extract. Beat until everything is combined.
Using two clean tablespoons, form the dough into eight walnut-sized balls.
Now make the dipping sauce: break the chocolate into small pieces and put into a small saucepan. Add the remaining sauce ingredients, then place over a low–medium heat and allow everything to melt, stirring regularly. Do not let it get too hot or the sauce will split.
When the oil is up to temperature, add half the dough balls to the pan and cook for two to three minutes, turning occasionally, until golden brown all over. Remove with a slotted spoon and drain on kitchen paper (paper towel). Cook the remaining balls in the same way.
Meanwhile, put the dusting sugar and cinnamon into a large bowl and mix together. Add the doughnuts and toss to coat.
Transfer them to a serving dish, grate over the orange zest and serve with the warm chocolate sauce.