Preheat your oven to 400°F. Place the sweet potatoes and yams on a foil-lined baking sheet. Melt 2 tablespoons of butter in the microwave, then drizzle it over the potatoes. Sprinkle with kosher salt and freshly ground black pepper, rolling the spuds around until they’re evenly coated. Roast until tender, which should take about 1 hour. Once done, let them cool.
While the potatoes roast, prepare the topping. Lightly spray a baking sheet, two spoons, and a mixing bowl with non-stick spray. Add the potato chips to the bowl and set it aside.
In a saucepan over medium-high heat, combine sugar, ½ tablespoon of butter, and ¼ cup water. Clamp on a lid, bring to a boil, and cook for 7 minutes. Remove the lid and continue to cook for 1 to 2 minutes until golden caramel forms. Do not stir! Just gently swirl the pan occasionally.
Remove from heat, stir in baking soda, kosher salt, and cayenne pepper, and drizzle over the potato chips. Toss to coat.
Transfer the topping to the baking sheet and spread it out evenly. Sprinkle with thyme and let it cool before breaking into smaller pieces.
Once the sweet potatoes are cool enough to handle, peel off the skins. Transfer the flesh to a stand mixer. Warm heavy cream and remaining butter in the microwave until melted, then combine with the potatoes, along with maple syrup, cinnamon, orange zest, and nutmeg. Beat until well combined.
Season to taste with kosher salt and freshly ground black pepper.
To serve, transfer the mashed potatoes to a large bowl and place the topping in a smaller bowl beside it. Let guests mix the two together as desired.
