Poke 3-5 tiny holes in each eggplant and place them on a baking sheet lined with parchment paper. Bake them for 1 hour. Flip them at around half time.
Take the roasted eggplants out of the oven and let them cool for 5-10 minutes.
Peel the eggplants and place them on a cutting board that is slightly tilted. Place the cutting board next to the sink to allow the liquid to drain into the sink. This step should take about 30 min to make sure that the eggplants are at room temperature and as much as the eggplant liquid as possible has drained. This liquid is bitter.
Oil-free plant-based mayo
Soak the cashews in hot water for 10-15 min.
Peel and cube the potatoes and carrot and boil them until tender.
Add all ingredients from the list, starting with the raw cashews, to a food processor and blend until a paste forms. This is the plant-based mayo.
Finalize the spread
Add the eggplants to the mayo and pulse several times to incorporate the veggies and form a uniform mixture. Do not over-process.
Mix the paste with minced onion. Add salt, pepper and mustard to taste.