Peel the yams well, then cut them into 2-3 inch chunks. Boil the yam chunks for 20-30 mins until soft when pierced with a fork. Let cool. Pass through a potato ricer into a large bowl.
Preheat the oven to 350 degrees. To the yams, add melted butter, maple syrup, vanilla, cinnamon, nutmeg, ground cloves, salt and pepper, mixing well. Pour in the heavy cream and coconut sugar, and use a hand mixer to whip the cream and sugar into the potato mixture. Grease a 9×12 pan with butter, then spread yam mixture into the pan, cover with foil, and bake for 20 minutes while you make the nut topping.
In a medium bowl, combine the pecan pieces and egg white, making sure the pecan pieces are evenly coated. In a smaller bowl, whisk together the coconut sugar, salt, cumin, Chinese five spice, and pinch of cayenne. Pour the spice mix over the pecans, mix together, making sure the spice mix is evenly coating the pecan pieces.
Remove the potatoes from oven, discard the foil, and pour the spiced pecan mix evenly over potatoes. Place back in the oven for 10 minutes or until the pecans are slightly browned and fragrant.