Preheat your oven to 425 degrees F. Line a sheet tray with parchment.
Cut the squash in half lengthwise and scoop the seeds. Peel the squash then place it on the prepared baking sheet. Drizzle with olive oil and rub the olive oil over the squash to evenly coat. Season with salt and pepper then place cut side up on the tray. Bake for 15 minutes, then flip and continue to cook until the squash begins to soften and get some color, about 5 minutes.
In the meantime, make the glaze. In a saucepan over medium heat, melt the butter. Brown the butter by allowing it to cook for an additional 2 minutes while swirling the pan occasionally. Add the herbs and briefly toast, about 30 seconds, then pour in the syrup, vinegar and chili flakes. Bring to a strong simmer and cook until reduced and thick enough to coat a spoon, about 2 minutes. Set aside.
Remove the squash from the oven and allow to cool slightly. When cool enough to handle, remove to a cutting board with the flat side down. Slice the squash, taking care not to slice all the way through. Place into a baking dish and pour half of the glaze over the squash, tucking the herbs between the slices.
Bake for 10 minutes then pull out of the oven and baste with the pan juices. Brush more of the glaze on then continue to bake for an additional 10 minutes, until the squash is cooked through. Brush on any remaining glaze, sprinkle with crunchy salt and serve.
To stop your knife from cutting all the way through the butternut squash, place 2 chopsticks along the length of each half before slicing.