Add the vegetable stock cube to the boiling water and stir in thoroughly.
Heat up a large frying pan over a medium heat, add 25g of the butter.
Once the butter has melted, add the onion and celery. Cook for 10 minutes until softened.
Stir in the rice, until the grains start to turn translucent at the edges.
Turn up the heat a notch to medium-high, adding in the white wine. Stir until all the wine has disappeared. Add the dried sage.
Slowly stir in the vegetable stock by adding in one full ladle at a time, stirring continuously until fully incorporated and the rice is cooked. Do this over the course of about half an hour.
Stir in the pumpkin puree and take off the heat. Place a lid on top and leave to rest for 5 minutes.
As the risotto rests, melt the other 25g of butter in a separate frying pan add the walnuts to toast.
Serve the risotto. Top with the crumbled roquefort cheese and buttered toasted walnuts.