Bring the potatoes and enough cold water to cover to a boil in a large saucepan.
Reduce the heat and simmer until fork-tender, about 20 minutes.
Drain and cool. Mash the potatoes in a large bowl until smooth.
Preheat the oven to 375°. Spray a 2 1/2-quart baking dish with nonstick spray.
In a small bowl, whisk together the milk, syrup, egg and vanilla in a small bowl.
Add the milk mixture to the potatoes, stirring to combine well. Stir in the raisins, coconut and 3/4 teaspoon salt until blended.
Spoon the mixture into the pan.
To make the topping, combine the brown sugar, flour, pecans, butter and 1/4 teaspoon salt in a medium bowl. Sprinkle the topping over the potatoes and bake, uncovered, until the center is hot and the topping is browned, 25 - 30 minutes.