Add a drizzle of oil to a suitably sized pan and begin frying mushrooms over medium heat. Once they brown on one side, flip them over until they get nice and brown on the other. It's important to get a nice char on each side of the mushroom to intensify the mushroom flavour. Don't just chuck them in a stir around, this will steam them and leave you with weak flavour. (see notes)
Season with a pinch of salt and pepper, then melt in butter and add garlic. Fry for a minute or so, then pour in chicken stock.
Allow the stock to simmer until it’s reduced by nearly half, then pour in your cream. Stir to fully incorporate, then add chives, parsley and a heavy pinch of salt & pepper (season well to bring out the best in this simple sauce). Allow to simmer a little longer until it begins to thicken (it will thicken, just keep it simmering).
Meanwhile, pop your pasta in salted boiling water and cook until al dente. Retain a cup of starchy pasta water.
When the sauce begins to thicken, stir in parmesan, then add pasta. If the sauce thickens too much, add a splash of pasta water to thin out slightly. You might not need to do this. If the sauce is still quite thin, continue to simmer and stir until it thickens.
Serve with a heavy sprinkling of parmesan and parsley!