Combine all dressing ingredients and whisk together. Thin with about 1 tablespoon of water, or until you reach desired consistency.
Remove outer leaves from romaine head until you reach the cluster of romaine heart (reserve the outer leaves for leftover dressing). Slice the head in half.
Set a heavy-bottomed skillet over high heat. Once hot, place the lettuce flat-side down in the pan and let cook without disturbing for 1-2 minutes, or until lightly charred. (You can add a bit of oil with a high smoke point--like avocado oil--to the pan before adding the lettuce, but I found it wasn't necessary.) Flip and repeat until the underside is also charred.
Immediately drizzle with dressing, garnish with sesame seeds, additional vegetables and anchovies, if using, and serve!