Once soft, add arborio rice. Stir the rice around so that all the grains are coated in oil.
Dissolve 2 heaped tablespoons of veg stock in a litre of warm water.
Now begin to add the veg stock liquid. About 500ml at a time. As half the liquid absorbs, add more liquid. When the litre of stock is finished, continue to add plain water, 500 ml at a time. In total, you should end up adding about 3 litres of liquid to fully cooking the rice.
To keep the rice from sticking to the bottom of the pot always keep enough water in the pot and stir regularly. Always stir clockwise.
When the rice is cooked, add the corn, peas, baby marrow and mushrooms.