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 sauce: In a small bowl or container, combine the sour cream, olive oil, lemon juice, rice vinegar, shallots, 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.
Notes
I like to let the squash cool slightly before drizzling with the dressing so the dressing doesn’t just immediately melt right into the squash. In fact, you should also consider letting the squash cool to just warm or even room temperature before dressing it. It makes for an interesting make-ahead side dish that way.
I have also served this with the sauce and torn fresh mint leaves and pomegranate ariels which was possibly my favorite version of this dish. Apologies for not having a photo - but trust me, it's gorgeous and delicious.