In a large pot of salted boiling water, cook the tagliatelle until al dente. Remove 1 cup (250 ml) of the cooking water. Drain.
In a large non-stick skillet over medium heat, melt the butter. Add the pasta, Bolognese sauce and half of the reserved cooking water. Reheat for 2 minutes, stirring to coat the pasta in the sauce. Add the cheese and adjust the seasoning. Add more reserved cooking water as needed.