Cook the tagliatelle in lightly salted water until al dente.
Melt the butter in a small pan and stir in the flour. Cook
the flour for a few moments and then add the cream all at once. Stir well with a balloon whisk and cook until the
sauce thickens and is free of lumps. Stir in the stock cube and season with salt and pepper.
Cook the bacon bits in a frying pan until all the fat has been released, remove from the pan, reserving the fat, and drain on kitchen paper. Use the bacon fat to cook the shallots
for 3-4 minutes. Remove the pan from the heat and stir in
the bacon, mushrooms and parsley. Add to the cream sauce and stir well. Drain the tagliatelle and stir into the sauce. Divide the tagliatelle between 4 plates.