Place stock in a heavy saucepan, and over medium heat bring to a simmer. Add saffron, stir, and leave to simmer very slightly.

Meanwhile, in a larger saucepan over medium heat, melt 1 tablespoon butter in olive oil. When foam subsides, add scallions and shallots, and cook, stirring frequently, until softened and yellow but not browned.

Add mushrooms and sauté, stirring occasionally, until liquid has evaporated. Add rice to mushrooms, and cook, stirring to coat well, with butter and oil.

Add the wine and stir until ¾ evaporated, then add approximately 3/4 cup of simmering stock to rice and mushrooms. Stir well and continue to cook, stirring occasionally, until rice has absorbed most of stock. Continue adding stock to rice by the half-cupful, adding only after rice has absorbed previous addition.

As cooking continues, you will have to stir more frequently. After 25 to 30 minutes, all the stock should be absorbed, and rice should be tender but still chewy.

Remove from heat. Add salt and pepper to taste. Stir in remaining butter and 3/4 cup of Parmigiano-Reggiano.

Serve immediately by using a large cookie cutter and mould risotto into cutter. Using a vegetable peeler, take 3 or 4 shaving off the  Parmigiano-Reggiano cheese and place on top of the risotto.