Cook the chicken breast and cut it in strips. Cook the fettuccine as indicated on the packet, drain. Put one portion of the butter on the pasta while it is still warm, or add a few drops of olive oil and stir so that the pasta doesn’t stick. Meanwhile, in a saucepan on a medium heat melt the butter, add the cream, garlic and merquén. Cook on a low heat for 20 to 30 minutes, stirring it so it mixes well. Add salt and pepper to taste. Remove the casserole dish from the heat and add the chicken and cheese. Serve it over the warm pasta, and sprinkle with freshly ground pepper and a parsley garnish.