In a saucepan, add butter and melt. Add the shallots and saute until translucent, about 3 minutes. Remove the pan from the heat and carefully deglaze with the cognac. Cook until the cognac is almost completely reduced. Add the chicken stock and heavy cream and citrus zest and cook until slightly thickened and reduced, about 10 minutes. Add cheese and season with salt and pepper.
While sauce is cooking, cook the pasta until al dente in boiling, salted water. Drain well.
Stir the mint into the sauce. Add the drained pasta and toss to coat the pasta well. Place the pasta on plates and sprinkle with the radicchio.
Yield: 4 servings