Melt butter in a large dutch pot or heavy-bottomed soup pot over medium heat, add carrots, onions, potatoes, and celery and sauté over medium heat until the veggies are slightly tender, about 6-8 minutes. Season the veggies with some salt.
Add the minced garlic, and sauté until fragrant, about 30 seconds.
Add tomato paste, lemongrass paste, sugar and cook for another 2 minutes.
Add the dry white wine, mix well. Cook for another 5 minutes.
Add the seafood stock, along with bay leaves, and thyme, mix well, lower the heat, and simmer for 15 minutes.
Turn off the heat. Discard the celery, bay leaves, and thyme stalks.
Blend the contents in the dutch pot with an immersion blender or wait for it to cool, transfer into a blender and blend the bisque in batches until you have a smooth pureé.
Return the bisque to low heat and add the heavy cream, stirring. Adjust salt and pepper. Simmer the bisque for another two minutes.
To sear the scallops: Remove the small side muscle from the scallops. Rinse with water and pat dry thoroughly with paper towels. Heat oil in a skillet until hot, but not smoking. Season the scallops with salt and pepper, place the scallops on the heated skillet, sear on one side for 1 & 1/2 to 2 minutes. Season the other side with salt and pepper, flip and cook the other side for another 1 & 1/2 minutes.
To serve scallop bisque: Ladle the bisque in a shallow bowl, place 1-2 scallops in the center. Drizzle some extra virgin olive oil or heavy cream if desired.