Start by filling a large stockpot (6-quart or bigger) with cold water. Add 1 tablespoon of kosher salt directly to the water—this seasons the potatoes during cooking rather than after, which means more even flavor distribution. Peel your sweet potatoes using a vegetable peeler, then cut them into ½-inch pieces. Aim for consistency here; uneven sizes mean some pieces overcook while others stay firm. Add the potatoes to the salted water, making sure they're covered by about 1 inch. This sounds like a lot of water, but it prevents the bottom pieces from scorching if the water level drops. Bring to a boil over medium-high heat, which usually takes about 8-10 minutes. Once you see rolling boils, reduce heat to medium and cover the pot. This keeps the temperature stable and prevents excessive evaporation. Set a timer for 15 minutes, then start checking. The potatoes should be tender enough that a knife slides through with slight resistance—you want to see them just barely holding their shape. They'll continue cooking in the oven, so stop here. If you go to 20-25 minutes (which many recipes suggest), you'll end up with mush. Drain immediately in a colander and let sit for 2 minutes to release excess moisture.

While the potatoes cook, preheat your oven to 350°F. Use a 9 x 13-inch baking dish; this is important because it affects both cooking time and the ratio of filling to topping. Lightly grease it with butter or cooking spray—don't skip this. Even with cream in the filling, sticking happens. The 350°F temperature is deliberately moderate. Higher heat caramelizes the top before the center heats through, and lower temperatures mean you're baking for nearly two hours. At 350°F, the filling sets gently while the streusel browns evenly.

Transfer your drained potatoes to the prepared baking dish. They should fill the dish to about ¾ of the way up; if yours looks different, that's fine—sweet potato sizes vary. Sprinkle with ⅓ cup brown sugar, 3½ tablespoons flour, and ½ teaspoon salt. Use your hands or a large spoon to gently toss everything together, distributing seasonings evenly. This is the moment to taste. Take a small piece, blow on it to cool it slightly, and taste it. It should be subtly sweet with salt underlying, not cloying. If it tastes flat, add a pinch more salt. This is your final seasoning check—you can't adjust after baking.

Pour the maple syrup evenly over the seasoned potatoes. Don't mix yet. Then pour the heavy cream in a steady stream all over the dish, making sure to reach the corners and edges. Now gently fold everything together 5-6 times with a spatula, turning the mixture from the bottom up. You want everything incorporated but not mushed. The cream will pool slightly; this is normal and creates the casserole's sauce as it bakes. This step literally takes 90 seconds, but it's where patience matters. If you stir vigorously, you'll break down potato pieces. If you don't fold at all, you'll have maple syrup pooling on top and potato on bottom.

In a medium bowl, combine 1½ cups chopped toasted pecans, 2 tablespoons flour, ¼ cup brown sugar, ½ teaspoon salt, 1 teaspoon cinnamon, and ½ teaspoon nutmeg. Stir with a fork until evenly distributed. Cut your cold butter into ½-inch cubes. Add it directly to the pecan mixture. This is the critical step for texture. Using just your fingertips (keep your hands cool; wash them first if they're warm), work the butter into the mixture by rubbing the flour and butter between your thumb and fingertips. You're creating friction that coats the flour with butter, which creates steam pockets during baking. Keep working until it looks like coarse sand—you should see pea-sized and smaller chunks of butter throughout. If pieces get larger than a pea, that's okay; they'll create crunchier clusters. If it turns into a paste, your hands were too warm. Pop it in the freezer for 5 minutes and try again.

Spread the streusel topping evenly over the potato mixture. It won't completely cover the filling, and that's correct—you want some filling visible between the topping clusters. This allows steam to escape and prevents sogginess. Place the baking dish on the middle oven rack (not the top, not the bottom). Bake for 55-60 minutes. You're looking for specific visual cues here, not just the timer. Peek at the 50-minute mark. The casserole is done when you see the filling bubbling actively around the edges and slightly toward the center, and the streusel is deep golden brown. If the topping is browning too fast (dark brown at 45 minutes), loosely tent with foil for the remaining time. If the filling still looks watery at 55 minutes, give it another 5 minutes. There's some variation based on your oven's personality.