Place 3 marrow bones, leg slice, carrots, onions and celery on a baking sheet, season with salt and pepper and roast on the middle rack at 180 ° C for about 30 minutes.
In the meantime, add water, apple cider vinegar, bay leaves, garlic and 3 marrow bones to the Instant Pot and let it steep.
After 30 minutes, add the roasted ingredients to the instant pot. Cook on the Soup - High Pressure - Normal program for 70 minutes.