see below

Butter for ramekins or baking dish (about 2 Tablespoons)
3 pounds yams
3/4 cup cream
1/ 4 cup pure maple syrup
1/4 cup (4 Tablespoons) unsalted butter for yams
1 Tablespoon kosher salt
1/3 cup brown sugar
5 Tablespoons butter, cut into small pieces
1/2 cup chopped pecans


Preparation

1Preheat oven to 375°F. Butter 9-inch x 12-inch gratin or baking dish.
2Bake Yams: peel yams and wrap in foil. Bake on a sheet pan until soft, about 1 hour. Let cool slightly. Transfer to a bowl and pass through a food mill or ricer.
3Prepare: maple mixture: bring cream and maple syrup to a simmer in a large saucepan. Add butter and stir until completely melted. Add the yams. Stir and turn off heat.
4Topping: in a food processor, combine butter and sugar. Pulse about 5-10 times. Transfer to a bowl and add the chopped pecans to butter mixture. Spoon yam mixture into gratin dish and smooth the top. Dot with the topping mixture. Bake for 15 minutes. Turn oven on broil and place under broiler for additional 1-3 minutes or until topping is slightly brown and bubbly (but be careful not to burn the pecans).