Roast the onions: Preheat the oven to 390F and line a rimmed sheet pan with parchment paper. Cut the onions (2) into wedges and transfer to the baking sheet. Toss with the olive oil (1 tablespoon), salt (1/8 teaspoon) and sugar (1/8 teaspoon), breaking the wedges up into individual petals as you stir. Roast the onions for 30 minutes, stirring every 10 minutes, until the edges are charred and the onions are soft. Set aside to cool.

Blend the dip: Once the onions are cool to the touch, pulse 2/3 of them in a mini food processor or blender with the garlic powder (1/8 teaspoon) and mayonnaise (1 tablespoon) until finely chopped. Add the sour cream (2/3 cup) and blend until you have an almost smooth dip.

Finish and chill: Roughly chop the remaining roasted onions on a cutting board. Stir them into the dip along with the chives (1 1/2 tablespoons, finely chopped), a little more salt (~1/8 teaspoon) and optional lemon juice (~1/2 tablespoon) to taste. Chill the dip for at least 4 hours, or preferably overnight before serving.

Serve and store: Serve chilled with a sprinkle of chives over the top for garnish. Pair with sea salt crackers or plain ruffled potato chips. Leftovers can be kept in an airtight container in the fridge for up to 4 days.