Melt butter in a large pot. Peel onion and cut into thin slices. Sweat the onions in the butter, but do not brown; stir regularly.
Heat cooking oil in a pan and add the onions, red chilli and curry leaves. Saute till the onions start browning on the outside. Turn off the heat and let cool.
Pour hot water over the currants and let drain.
Transfer to a mixer, add salt, water and grind well. Pour coconut oil to the chutney, stir well and serve with hot dosas or idlis.
Finely chop the apples and currants, and simmer with the onions, wine, syrup, vinegar and sugar for about 1 hour over a medium heat, until the excess liquid has boiled off. Cool and pour into jars. Keep refrigerated.