Preheat the oven to 400°F. Place the squash on a rimmed baking sheet, drizzle over the melted butter, sprinkle over the sugar, season with salt and pepper and toss to combine. Spread out in a single layer on the baking sheet, allowing space in between the cubes when possible. Roast for about 25 minutes until tender and lightly browned on the bottom.
Meanwhile, make the dressing. In a small bowl of container combine the sour cream, olive oil, lemon juice, rice vinegar, shallots, and salt and pepper.
When the squash is roasted, let it cool slightly for 5 to 10 minutes. Transfer to a serving dish and drizzle over the dressing. Sprinkle with the herbs and serve immediately.