Preheat oven to 450°F. Line a large rimmed baking sheet with parchment paper. Stir first 3 ingredients in a large bowl until sugar dissolves. Add pineapple; toss to coat. Let marinate, tossing occasionally, for 10 minutes. Place pineapple, one flat side down, on prepared sheet; reserve marinade.
Roast pineapple for 15 minutes. Turn, brush with marinade, and roast until tender and caramelized, 10-15 minutes. Drizzle remaining marinade over; let cool slightly.
Divide pineapple among plates. Spoon crème fraîche alongside. Garnish with nuts and mint.
Per serving: 283 calories, 5 g fat, 60 g carbohydrates Nutritional analysis provided by Bon Appétit