Place a 10-inch carbon steel pan in the middle of the oven and heat the oven, with the pan in it, until it hits 350ºF. Leave the oven on for at least 30 more minutes after it comes to temperature.
While the oven is heating, measure the butter out onto a square piece of parchment measuring about 2 inches by 2 inches. Let it sit near the stove to warm up; you want the butter to be very soft, but not melted.
After 30 minutes, in a medium bowl, whisk together the mayonnaise, water, harissa or herbs (if using), and salt until smooth. Whisk in the eggs until a light and homogenized mixture is formed. Pull out your serving bowl(s) or plate(s) and place them near your cooktop.
Remove the pan from the oven and place it on a burner over medium heat. Add the butter and swirl the pan to coat.
As soon as the butter melts, pour in the egg mixture and count to 10. Stir just twice with a rubber spatula and count to 10 again. Stir two more times, then count to 5. Stir three final times to get any remaining liquid down into the pan, count to 5, then immediately transfer the finished eggs to plates. You should still see some runny eggs in the pan — these will continue to cook in your serving vessel. If not using harissa, top with black pepper. Consume. Note, please, the silky texture and hint of spice. Have a nice day.