Pour stock and water into a saucepan, add porcini mushrooms and bring to a simmer over a medium heat for 5-7 minutes or until mushrooms have rehydrated. Remove mushrooms with a slotted spoon, chop and set to one side. Leave stock simmering over a low heat.
Melt 20g butter in a frying pan over a high heat, add oil and pancetta and cook for 2-3 minutes, rendering out the fat. Transfer pancetta to a plate. Add eschallots, celery and sage to the same pan and cook gently until translucent.
Stir in rice and pan fry for 2-3 minutes, stirring continuously. Pour in wine, cook until evaporated and add mushrooms, stirring to combine.
Pour in stock, ½ cup at a time, allowing each addition to be completely absorbed before adding the next, stirring continuously until liquid is absorbed and rice is al dente.
Pour in stock, ½ cup at a time, allowing each addition to be completely absorbed before adding the next, stirring continuously until liquid is absorbed and rice is al dente.
Return pancetta to the pan, add half the parmigiano and the parsley and mix to combine.
To serve, spoon risotto into bowls and top with remaining parmigiano.