Place the finely sliced cabbage in a large bowl and add the onions and the salt. Use your hands to thoroughly massage the cabbage for a few minutes until it's broken down. The volume should be reduced by almost half and there will be a pool of water at the bottom of the bowl. Cover the cabbage and let it sit for 30-60 minutes to allow the salt to draw out the excess water.Place the cabbage in a colander and give it a thorough rinse.Let it drain in the colander for another 30 minutes, squeezing out as much of the water as you can.
To make the vinaigrette, place all of the ingredients in a small bowl and whisk to combine.Place the drained cabbage in a large bowl. Pour the vinaigrette over the cabbage and stir to thoroughly combine. Cover and refrigerate the Krautsalat for at least 4 hours for optimal flavor. You can serve it cold or at room temperature.Store in the fridge where it will keep for 2-3 days. It's still edible beyond that but the cabbage will become discolored.