Cook the potatoes in a large pan of boiling water for about 20 minutes, or until soft.
Drain and peel off the skins, then set aside.
Cook the peas in a separate pan of boiling water for about 5-7 minutes, or until tender, then set aside.
Mix the mustard powder, turmeric, chilli powder, fenugreek leaves and vinegar together in a bowl, then season with salt.
Heat the oil in a large pan over medium heat.
Add the garlic paste and stir-fry for about 1-2 minutes, or until it turns light golden.
Add the ginger paste and stir-fry for about 1-2 minutes, or until light brown.
Add the vinegar with the spices.
Then add the peas and potatoes and cook for about 1 minute.
Mix well, remove from the heat and allow to cool.
When cool, bottle into sterilized jars and leave for 1-2 days.