Heat a browning dish in the microwave oven for 6-8 minutes, following the manufacturer's instructions.
Mix half of the cornstarch (cornflour) with the nuoc mam and vinegar to a smooth paste.
Add the sugar, garlic powder, fivespice powder, several dashes of tabasco sauce and a little salt and pepper.
Mix well.
Add the meat and stir until all the cubes are well coated.
When the browning dish is hot, add the butter and oil, taking care to avoid spattering the inside of the oven.
Tilt the dish so that the base is completely covered with fat.
Put the meat cubes in the dish side by side.
When they stop sizzling, turn to seal on all sides.
Microwave, uncovered, for 3 minutes on HIGH.
Mix the sherry and the remaining cornstarch (cornflour) in a cup.
Transfer the meat with a slotted spatula to a warmed serving dish.
Add the sour cream (creme fraiche) to the browning dish and stir with a wooden spoon until the cooking sediments are fully dissolved.
Pour into the cup containing the sherry.
Stir well and heat in the oven for1 minute on HIGH.
Stir, pour over the meat, sprinkle with chopped chives