Set the oven temperature to 375 degrees F and coat the inside of an 8x8-inch baking dish with non-stick cooking spray.
Transfer the drained yams into a large mixing bowl and proceed to mash them.
Include brown sugar, syrup butter, salt, cinnamon, nutmeg and vanilla extract. Mix thoroughly.
Evenly distribute the mixture in the baking dish, ensuring it covers the entire surface. Add a layer of pecans on top, followed by a generous topping of marshmallows.
Allow to bake for a period of 20 minutes, or until the marshmallows have reached a desirable level of toasting.
Notes
Different Nuts: If you're not a fan of pecans, feel free to use different chopped nuts like walnuts or almonds for a delightful twist.
Extra Toasty Marshmallows: For extra toasty marshmallows, broil the casserole for about 2 minutes after baking until the marshmallows reach your desired level of crispiness.
Garnish with Caramel Drizzle: For a decadent touch, drizzle some warm caramel sauce over the finished casserole just before serving.