The enzyme that decides how sweet your sweet potato tastes
Here is the thing that separates a sweet potato from an ordinary one, and it has almost nothing to do with the variety you bought. A sweet potato is packed with starch, and it carries an enzyme that slowly converts that starch into maltose, a sugar, as the potato heats. The catch is that the enzyme only works in a moderate temperature window on the way up, roughly 135 to 170°F, so the longer the flesh lingers there, the more starch becomes sugar and the sweeter the potato tastes. This single fact explains why a slowly baked sweet potato comes out of the oven tasting like candy while one you microwaved in seven minutes tastes flat and starchy: the fast cook blew straight past the window before the enzyme could do its work.
That is why the method you choose is really a choice about sweetness. A long, slow bake gives the enzyme the most time and yields the deepest, most caramelized sweetness, the drips of dark syrup that leak onto the pan are literally that sugar. Roasting cubes or wedges in a hot oven caramelizes the surfaces for concentrated flavor. Boiling and steaming, which move quickly and cook at or below the boiling point, build far less sweetness and instead give you a milder, cleaner potato, which is exactly what you want when it is a component in something else. None of these is wrong; they are different tools for different results.
Boiling and steaming, the fast lane
When you need sweet potatoes tender quickly, for mash, for a soup, for a salad, boiling and steaming are the way, and the timing is simple once the pieces are even. To boil, scrub the potatoes, cut them into uniform 1-inch chunks (peel now or slip the skins off after), start them in cold salted water, and simmer until a fork slides in easily, about 12 to 15 minutes for cubes. Whole unpeeled sweet potatoes take much longer, roughly 30 to 50 minutes depending on size. The one rule is to drain them thoroughly, since waterlogged flesh makes a loose, bland mash.
Steaming is the quiet upgrade, especially for mashing. Because the pieces sit above the water instead of soaking in it, they come out drier and more flavorful, so the mash tastes more like sweet potato and less like water. Steam even chunks over simmering water for about 15 to 20 minutes until tender. Boiling is a touch faster and heats very evenly, which makes it convenient, but if you care about flavor and a firm, scoopable mash, reach for the steamer basket. Either way, these methods trade some sweetness for speed, so lean on butter, salt, and spices to season what the cooking did not build.
Storage, and the cold-damage trap
Sweet potatoes want the same cool, dark, ventilated pantry that regular potatoes do, around 55 to 60°F, in a basket or paper rather than a sealed bag. But they are even less tolerant of the fridge. Where a cold-stored regular potato just turns sweet, a cold-stored sweet potato suffers real chill damage: it develops a hard core that stubbornly refuses to soften no matter how long you cook it, along with off-flavors. So keep them out of the refrigerator entirely until they are cooked. Stored properly they will keep for several weeks, and unlike many vegetables they get a little sweeter with a week or two of curing time. The per-method guides below cover baking, roasting, air-frying, steaming, and boiling in detail.