Heat the olive oil in medium saute pan over medium heat. Add sliced onions to the pot. You should hear a moderate sizzle. Sauté the onions, stirring often, until they are just starting to soften on the edges. Then, lower the heat slightly. Keep cooking and stirring the onions occasionally until they are golden brown, jammy, and super sweet. This process will take anywhere from 40 minutes to an hour. Add splashes of water if the onions start to dry up/stick. Transfer the caramelized onions to a cutting board and chop them up nice and fine.
Drain the cashews and add them to an upright, high speed blender. To the cashews, add the water, lemon juice, apple cider vinegar, and sea salt. Blend the mixture on high for a full 2 minutes, stopping the motor to scrape down the sides of the blender if necessary. The resulting “sour cream” should be completely smooth.
Scrape the cashew sour cream into a medium bowl. To the sour cream, add the chopped up caramelized onions, onion powder, tamari, lots of salt, and pepper. Stir until the dip is evenly mixed. Taste the dip for seasoning and adjust if necessary. Store the dip in a sealed container in the fridge until ready to use (and up to 5 days).
Make the fresh za’atar. In a small bowl, combine the minced thyme, sumac, sesame seeds, and a pinch of salt. Stir to combine.
To serve the vegan caramelized onion dip: scrape the dip out into a shallow serving bowl. Make swoops and swirls with the back of a spoon. Drizzle the top of the dip with olive oil (or chili-infused olive oil). Sprinkle all of the fresh za’atar on top of the dip. Finish with flaky sea salt if you like. Serve the dip with potato chips, cut vegetables, or crackers.