Place the foie gras in a baking dish, pour 2 cups cognac over, and set aside to marinate for 30 minutes.

Meanwhile, prepare the risotto: Slice 2 of the shallots, chop the other 2, and set aside. In a deep skillet over medium-high heat, melt the butter. Add the chopped shallots, and sauté for 5 minutes. Add the rice, and toast, stirring, for 3 more minutes. Stir in 3 tablespoons cognac, season with salt, and cook until the cognac evaporates. Add the beef stock in ½-cup increments, allowing each addition to be absorbed before adding more. Cook, stirring, until the rice is tender and creamy, about 20 minutes.

Meanwhile, carefully press 2 shallot slices onto each piece of foie gras. Add to a nonstick skillet over medium-high heat, and sauté for 1 minute on each side. Remove from the skillet, and set aside. Add the celery to the skillet, season with salt, and deglaze with 1 tablespoon cognac. Cook for 8 minutes, or until the celery is tender.

Stir the Parmigiano-Reggiano into the risotto, along with the remaining 1 tablespoon cognac. Divide the risotto among individual plates, and top with some of the celery and a slice of foie gras. Finish with a grinding of pepper, and garnish with marjoram.