Place the potatoes, water, onion and stock in an ungreased microwave-safe 2 1/2 litre dish. Cover and microwave on high for 12-14 minutes until potatoes are tender and the stock is dissolved, stirring once.
In a small bowl, combine the flour, salt and garlic; stir in milk until smooth. Pour over potatoes. Microwave, uncovered, on high for 4 minutes or until thickened, stirring twice.
Stir in sour cream; sprinkle with cheese. Cook 3 minutes longer or until cheese is melted.
Recipe works very well in the microwave so handy for when I have something else cooking in the oven because my oven doesn't cope well with more than one thing at once. I would not put the extra salt in it next time because I found the stock powder added enough but greatly enjoyed. - 18 Aug 2012