In a large skillet, heat olive oil over medium heat. Saute the onion for about 10 minutes, or until soft and slightly caramelized.
While the onions are cooking, slice the cauliflower. Place half of the cauliflower in a food processor using the "S" blade. Slowly pulse until it becomes the texture of rice but be careful not to over-process lest you be left with cauliflower mush. Process to the point where there is still a bit of texture to it. When the first half of the cauliflower is pulsed to perfection, put it in a big bowl and then add the remaining half. Again, pulse to perfection.
Now it should be time to add the celery to the onions and saute for 3-5 minutes.
Add 1 more tablespoon of olive oil just before you add the cauliflower to the skillet, stir to coat and cook 5-10 minutes. Taste it after 5 minutes to see if you like the texture or whether it needs a bit more cooking time. (I cooked mine about 8 minutes.) When it's cooked to your liking, add the salt and stir to combine.
Serve immediately. When plating, drizzle with a little extra virgin olive oil, a pinch of salt and a few grinds of black pepper.