I find it hard to put into words what impact mustard seeds have. The best way of appreciating their unique mildness is with something very simple. These green beans are transformed by their presence and I would be happy to serve them with any non-Indian dish. If you can find a word to do justice to mustard seeds and to describe their mystical effect, let me know.
Blanch the beans in a pot of boiling water for 3 – 4 minutes, or until they are just tender but still with a nice bite. Drain immediately in a colander. If you are preparing the green beans in advance, plunge them directly into cold water, leave for a few minutes till cold and then drain. The beans may be blanched ahead of time.
Heat the oil in a large frying pan. When hot, add in the mustard seeds. As soon as they begin to pop, add the garlic and the red chilli. Stir for a few seconds. Put in the green beans, salt and sugar and stir to mix. Turn down the heat to low and cook the beans, stirring regularly for 7–8 minutes, until they have absorbed the flavour of the spices. Serve immediately.