Place the mustard seeds in a medium glass or ceramic bowl along with the vinegar and grape juice. Mix in the salt and cumin seeds. Set aside, covered (but not sealed airtight), for 36 to 48 hours.
Place the mixture in a food processor and process for 1 to 2 minutes, until the seeds are coarsely ground (a mortar and pestle works here as well). Add the almonds and pine nuts and pulse a few times just until the nuts are completely broken up, being careful not to over-process.
Adapted from The Mustard Book by Rosamond Man and Robin Weir.