Cook the pasta in boiling salted water as per the packaging instructions until al dente, drain.
Heat the oil in a pan, sauté the leek for approx. 2 mins. Add the Brussels sprouts and cook for approx. 1 min. Add the stock, bring to the boil. Reduce the heat, simmer over a low heat for approx. 5 mins. Add the soy cream, horseradish mousse, lemon zest and juice, mix, season. Plate up the pasta and sauce together.