Preheat the grill to 350 degrees F. Peel and slice the butternut squash into 1 to 2-inch wedges. Place in a large bowl and season with the maple syrup and Chinese 5-spice powder. Grill the squash until grill marks appear, about 4 minutes per side. Set aside to cool. Meanwhile, crush the coriander seeds in a mortar and pestle. Heat the olive oil in a large pot over medium-high heat and add the onions. Cook until soft. Add the coriander and red pepper flakes and cook until the onions are barely caramelized, about 10 minutes. Add the grilled squash and chicken stock and bring to a boil. Lower the heat to medium and simmer for 15 to 20 minutes to help the flavors develop. Take the soup off the heat and blitz in a blender until smooth. Season with salt and pepper, to taste. If the soup gets too thick, add more chicken stock to thin it out. Chiffonade half the sage leaves, leaving the other half whole. Fry all the sage leaves in a pan of hot olive oil until the leaves are crispy and still green. Ladle the soup into cups, top with 1 teaspoon creme fraiche, and garnish with fried sage and porcini salt.