Sweet Potato Casserole

Method

1. roast55 min
   400°F, whole, until collapsing
   sweet potatoes whole in their skins until a squeeze meets no resistance — roasting drives moisture out and concentrates the sugars where boiling washes both away; the deep caramel note of a good casserole starts here or never
2. mash6 min
   flesh scooped hot, half the butter in first
   the flesh + half the butter melting on contact, then warm milk + eggs + vanilla + salt + cinnamon whipped smooth — the eggs are the difference between a casserole that slices and a puddle of mash wearing a topping; taste before adding ANY sugar to the base, because roasted sweet potatoes usually need none
3. mix3 min
   the streusel, rubbed to clumps
   brown sugar + flour + pecans + the remaining butter (cold, cubed) rubbed with fingers until it clumps like wet sand — the flour is what keeps the topping crumbly instead of melting into candy glass
4. bake30 min
   350°F, streusel over the filled dish
   until the topping browns and the center puffs slightly — the eggs are setting a light soufflé under the crunch; marshmallow partisans add theirs for the final 10 minutes only, until bronzed, because marshmallows in from the start are a black lacquer by minute twenty
5. rest10 min
   before serving — like every custard-set dish it firms as it cools, and it reheats gracefully, which is why it is the one Thanksgiving side worth making a day ahead