For the yams: Preheat the oven to 400 degrees F. Toss the yams with the oil in a medium bowl and sprinkle with salt and pepper.
2. Melt 2 tablespoons of the butter in a small saucepan over medium heat. Add the brown sugar, honey, cinnamon, vanilla and nutmeg and cook, stirring, until the mixture comes to a simmer and the sugar dissolves, 4 minutes. Remove from the heat, add to the yams and toss to coat.
Spread the yams and all the sauce evenly into a 9-by-13-inch baking dish. Cover tightly with foil and bake until beginning to become tender, 30 minutes.
For the crunch: Meanwhile, pulse the gingersnaps in a food processor until they are fine crumbs with a few larger pieces. Transfer to a medium bowl and stir in the sugar, butter and flour to combine. Form crumbles in several sizes using your hands and chill in the refrigerator.
Remove the foil from the yams and stir to coat with the sauce. Continue baking uncovered until the potatoes are tender and the sauce has thickened, 20 to 25 minutes. Top with gingersnap crumbles and bake until the yams are very tender and the topping is nicely browned, about 10 minutes longer. Serve.