Place sweet potatoes in a large pot and cover by 2-3 inches of water.
Bring to a boil over medium high heat.
Boil until completely tender.
Drain sweet potatoes.
Transfer potatoes to a large mixing bowl and add milk, butter/oil, syrup, salt, vanilla, and egg.
Mash or use immersion blender to mix until smooth.
Pour mash into an oiled 8 × 8 or 2-quart baking dish and smooth the surface.
When ready to bake, preheat the oven to 375°F degrees and make the topping.