Preheat the oven to 425°F and line a rimmed baking sheet with parchment paper or aluminum foil. Use a fork to poke holes into the sweet potatoes, and set them on the baking sheet.
Roast for 45 to 50 minutes, flipping over half way, until the potatoes are oozing a bit and you can easily pierce them with a fork.
When cooked, remove from the oven and let cool until you can handle them. Set the oven to broil on Hi and make your miso butter.
In a small saucepan, melt the butter over medium low heat until melted. Add in the miso and whisk to incorporate. The miso will still be a bit clumpy and that’s okay.
Slice the sweet potatoes in half lengthwise and keep on the baking sheet. Brush each half with the miso butter, getting all those miso bits onto the potatoes. Sprinkle lightly with Kosher salt.
Broil for 3-5 minutes until the tops have turned to a light golden brown.
Remove and let cool for 5 minutes. Serve and enjoy!