Bring the stock to a slow, steady simmer.Put the shallots in a heavy-bottomed casserole with 25g of the butter and all the oil, and saute over medium-high heat until translucent but not browned.
Add the rice and stir until it is well coated. Saute lightly, then add 150ml of the simmering stock and stir while cooking, until the rice absorbs the liquid and wipes the sides of the pot as you stir.
Add another 150ml of stock as the rice dries out, and stir it very frequently to prevent it from sticking.When you estimate that the rice is about 5 minutes away from being done, add all the grated cheese and the remaining butter.
Mix well. Check salt. Remember, when the cooking nears the end, not to add too much stock at one time. The risotto should be creamy but not runny. Serve immediately, with additional grated cheese, if desired.