1. PREHEAT the oven to 375°F. Melt the butters over low heat on the stove top, then mix together with olive oil and set aside.
2. PEEL the sweet potatoes, then slice crosswise as thinly and evenly as possible (between 1/8” and 1/16” is ideal). A mandoline will make the task far easier.
3. BRUSH a healthy coating of the butter and oil mixture over the inside of an 8” or 9” baking dish or skillet and sprinkle with a pinch of coarse sea salt. Arrange the potatoes in the dish, brush with the remaining butter and oil and sprinkle with the remaining salt.
4. ROAST the potatoes for 1 hour and 15 minutes, or until the middle of the potatoes are tender and the tops begin to brown and crisp. (The exact time will depend on your oven and on how thinly you’ve sliced the potatoes. Test them with a fork to make sure they’re tender in the middle.) Remove from the oven and let rest for 10 minutes. While the potatoes are resting…
5. WHISK together the coconut milk, crème fraîche, and sriracha in a saucepan over medium heat, until just warmed.
6. POUR half of the sauce over top of the potatoes and sprinkle with half of the minced cilantro. Combine the remaining sauce and cilantro and serve alongside the potatoes, for guests to use as desired.
*Sriracha, pronounced see-RAH-jah, is a Thai hot chili sauce. It is made from red chiles, distilled vinegar, garlic, sugar and salt; and is aged for three months or longer. Unlike American hot sauces such as Tabasco, which are vinegar sauces that are infused with hot chiles, sriracha is primarily puréed chiles, making it a much thicker sauce. The sauce is named after the coastal city of Si Racha in eastern Thailand, where it was first made and marketed.