Once most of moisture has dried out, add packets of mushroom sauce and mix until you have a paste.
Tip: You'll need to add the cream fairly soon after doing this, otherwise your 'paste' won't dissolve, and you'll end up with lumps of mushrooms in cream instead :-)It takes a bit getting used to. If you're struggling with this, then feel free to add the packets of sauce the the mix after you've added the cream.
Add cream and bring to a boil, reduce heat, stirring frequently until sauce thickens.
Tip: If your sauce get too thick, add some full cream milk to the sauce and stir until you have a smooth sauce again.