Cook the spaghetti in boiling salted water for 5 minutes, until "al dente."
Meanwhile, pour some of the extra virgin olive oiloliveoil into a saucepan; add the sliced green onions and chopped celery. Add the vegetable broth and cook gently for 3 minutes. Remove from the heat.
In a hot non-stick skillet, sauté the foie gras in pieces with the butter and rosemary. Cook the foie gras for two minutes so that a nice crust is formed on the outside, while the inside remains soft and creamy. Remove from the pan and keep warm on paper towels.
When the spaghetti is ready, combine with the vegetable sauce, mix in the porcini and foie gras and serve very hot. Garnish with basil florets or small basil leaves.