Place the cubed sweet potatoes in a large pot and cover with cold water by at least 1 inch. Add 1 tablespoon of salt. Bring to a rapid rolling boil over high heat, then reduce heat to medium and simmer vigorously for 14 to 16 minutes until fork-tender and yielding effortlessly. Drain thoroughly in a colander and let steam dry in the warm pot for 2 minutes to eliminate excess moisture.

While the potatoes boil, melt 4 tablespoons of butter in a light-colored stainless steel skillet over medium heat. Swirl the pan continuously as the butter melts, foams, and crackles. After 3 to 4 minutes, golden-brown toasted milk solids will form on the bottom with an irresistible nutty aroma. Immediately remove the pan from the heat and pour into a heat-safe ramekin to halt cooking.

In the same warm skillet over medium-low heat, melt the remaining 2 tablespoons of butter. Stir in the chopped pecans, brown sugar, flour, 1/4 teaspoon cinnamon, and a pinch of salt. Cook, tossing frequently, for 3 to 4 minutes until the pecans are crisp, fragrant, and coated in a glossy, bubbly candied glaze. Transfer to parchment paper to cool.

Mash the hot sweet potatoes using a potato masher or hand mixer until smooth. Pour in the prepared nutty brown butter (reserving 1 teaspoon for drizzling), warmed cream or milk, pure maple syrup, remaining cinnamon, nutmeg, sea salt, and black pepper. Whip on medium-high speed for 60 to 90 seconds until silky, airy, and cloud-like.

Spoon the velvety whipped sweet potatoes into a warm shallow serving bowl, creating elegant swooshes with the back of a spoon. Crown the center with the crunchy spiced pecan streusel, drizzle with the reserved brown butter and an extra ribbon of maple syrup, and scatter with fresh thyme leaves. Serve immediately.