Using a knife, prick the sweet potatoes. Put on a cookie sheet and bake for 1 hour (or until they are soft). Remove from the oven and let rest for a few minutes.
Peel the sweet potatoes. Put them in a food processor, along with butter, maple syrup and sour cream and mix to obtain the consistency of a puree.
Put the puree in a bowl, add chives, gently mix together, then put the roasted pecans on top and serve.