Special equipment: a pastry cutter
For the sweet potatoes: Preheat the oven to 375 degrees F.
Bake the sweet potatoes until fork-tender, 30 to 35 minutes. Remove the potatoes and raise the oven temperature to 400 degrees F.
Slice the sweet potatoes in half and let them cool slightly. Scoop out the innards, place into a large bowl and give them a good mash, leaving some texture to the potatoes--no need to mash completely. Add the granulated sugar, milk, salt, vanilla extract and eggs. Stir and mash the mixture around--you don't want them to be perfectly smooth.
Butter a 2-quart baking dish, pour in the potatoes and smooth out the top.
For the topping: Combine the brown sugar and flour in a bowl. Throw in the butter and with a pastry cutter, cut together until thoroughly combined. Add the pecans and combine until the topping is nice and crumbly. Sprinkle the crumb mixture all over the top of the potatoes.
Bake until golden brown, about 30 minutes.