Special equipment: six 6-ounce ramekins
Combine the clams and 2 cups water in a large pot and sprinkle with salt and pepper. Cover and cook over high heat until the clams open, 5 to 10 minutes. With a slotted spoon, remove the clams to a bowl. When cool enough to handle, remove the meats from the shells and roughly chop the clam meats.
Strain the clam liquor through a fine mesh sieve lined with a paper towel and set aside.
Rinse out the pot and set it over medium-high heat. Add the olive oil and bacon and cook until crispy, about 3 minutes per side. Remove the bacon to a plate. Add the carrots, celery, garlic, potatoes and onions to the pot and cook until the veggies begin to soften, about 5 minutes. Add the cornstarch and flour, stir to combine, then add the butter. Cook until the butter is fully absorbed and the flour and cornstarch have turned the color of peanut butter, 2 or 3 minutes. Add the half-and-half and reserved clam stock, and reduce the heat to medium low. Cover and simmer until the potatoes are easily pierced with a fork, about 20 minutes. Taste and adjust the seasoning with salt and pepper. Add the reserved clams (they will warm up in the soup).
Preheat the boiler.
Chop the bacon and mix it together with the panko, chives and lemon zest in a small bowl. Set the ramekins on a baking sheet and divide the soup among the ramekins. Sprinkle each with the panko mixture. Transfer the baking sheet to the broiler and broil until the panko begins to brown, about 30 seconds. Garnish with chopped tarragon and serve!