Preheat the oven to 400 degrees F. Arrange a rack inside a large roasting pan and set aside.
Season the chicken both inside and out with the kosher salt and black pepper.
In a small bowl, combine the honey, lemon zest and juice and butter. Place the chicken on a rack in a roasting pan breast side up and roast until lightly browned, about 15 minutes. Using a pastry brush, brush half of the honey mixture over the chicken, as well as sprinkling half the thyme over the chicken and return the chicken to the oven. Continue to cook another 30 minutes, or until an instant-read thermometer inserted in the thickest part of the thigh registers 180 degrees F. Remove the chicken from the oven and brush the remaining honey blend and sprinkle the remainder of the thyme over the chicken.
Remove the chicken from the oven and transfer to a platter or cutting board to rest for 10 minutes before carving.
To serve, spoon the sweet potatoes into the center of 4 large plates and arrange the chicken on top. Drizzle the chicken with any remaining pan juices and serve immediately with the sweet potatoes.
Preheat the oven to 350 degrees F.
Place the potatoes on a foil lined baking sheet and bake until tender and begins to ooze sugary syrup, about 1 hour and 15 minutes. Remove from the oven and let sit until cool enough to handle.
Cut the potatoes in half lengthwise and scoop out the flesh with a spoon into a large bowl. Add the cream, sugar, butter, syrup, salt and pepper, and thyme, if using and mix, mashing until the potato mixture is smooth. Cover to keep warm until ready to serve.