Heat the butter in a medium saucepan or Dutch oven over medium heat. Add the onions and garlic and cook until soft. Stir in the sweet potato puree and salt and pepper and cook until the puree is slightly thickened (you are making a sort of sweet potato roux). Increase the heat to high, add the wine and cook until completely reduced. Add the clam juice and cook for 15 to 20 minutes, stirring occasionally. If the mixture appears to be too thick, thin with a little extra clam juice or water, season with salt and pepper. Strain the mixture into a bowl and return to the pan.
Heat the butter in a small saute pan over medium high heat. Add the potatoes and cook until golden brown and caramelized. When the potatoes are almost cooked through, sprinkle with the sugar and toss until the sugar is dissolved and the potatoes are cooked through. Remove with a slotted spoon to a plate lined with paper towels.
Heat a pan over medium heat, add the bacon and cook until golden brown and crisp. Remove with a slotted spoon to a plate lined with paper towels.
Bring wine to a boil in a medium saucepan, add the clams, cover and cook until all clams open, discarding any that do not, about 4 to 5 minutes. Remove the clams with a slotted spoon and place in a bowl.
Bring sweet potato chowder base to a simmer. Add the cooked bacon, sweet potatoes and honey and cook for 1 minute. Add the chopped clams and cook for 2 minutes. Add the heavy cream and cook an additional minute or until just heated through. Ladle into bowls and garnish each bowl with 3 clams in the shell and a sprinkling of fresh tarragon. Serve immediately.
*to roast sweet potatoes, preheat an oven to 375 degrees F. Roast the potatoes for 45 minutes to 1 hour, or until soft.