This is a staple when I'm cooking a midweek dinner and want to make it "nice". It comes in two versions, and you can experiment to make others. Ingredients are for 2 people.
2 small shallots, or 1 larger one. Onions probably won't work.
40ml (a large splash) of white wine.
120ml of single cream - UHT is fine.
Pinch of chicken stock powder (¼ of an Oxo cube - if not, use a pinch of salt).
Version A: 2 teaspoons of green peppercorns (they come in a jar preserved in brine), crushed with a rolling pin or in a pestle and mortar.
Version B: 3 teaspoons of Dijon mustard, or to taste.
Method: Peel and finely chop the shallots. Sweat them for 4 or 5 minutes over a low heat in a small frying pan with a little olive oil or butter. Add the wine and turn up the heat to medium. Cook until most of the liquid has gone, stirring occasionally. Turn the heat back down. Add the chicken stock powder and the peppercorns or mustard. Stir to mix. Turn the heat as low as possible (maybe use a diffuser) and stir in the cream. Let it get hot but not boil, stirring from time to time.
Serve immediately with (version A) grilled salmon steaks or (version B) pork chops, which you have been cooking in the oven while you made the sauce. For a Masterchef-style touch, warm the plates and put the sauce on first, then serve the fish/meat on top.