Rinse the fingerling potatoes under cold water and brush off any dirt. Trim any rough ends. If potatoes are larger than 1 inch thick, halve them lengthwise so most pieces are similar size; leave small ones whole.

Place the prepared potatoes in a medium saucepan and add enough cold water to cover by about 1 inch. Add 1 tablespoon coarse kosher salt. Bring to a gentle boil over medium-high heat, then reduce to a simmer and cook until potatoes are just tender when pierced with a knife or skewer, about 12–15 minutes depending on size.

While the potatoes cook, prepare an ice bath: fill a large bowl with 2 cups ice and cold water. When potatoes are tender, immediately drain them in a colander and transfer to the ice bath to stop cooking for 2–3 minutes. This preserves texture and color. Drain thoroughly and pat dry with a kitchen towel or paper towels.

Make Dressing & Finish

Melt the butter in a small skillet over low heat or microwave briefly until softened. In a medium bowl whisk together 2 tablespoons olive oil, melted butter, 1 teaspoon lemon juice, 1 teaspoon white wine vinegar, 1/2 teaspoon Dijon mustard and 1/2 teaspoon honey or maple syrup until emulsified.

Add scallions: Separate the white and green parts of the scallions. Thinly slice both; add the white slices to the warm dressing first so they soften slightly, and reserve most of the green slices for garnish. Add the reserved white and most of the green scallion slices to the bowl. Add 1 tablespoon finely snipped chives if using.

Season the dressing with 1/2 teaspoon salt and 1/4 teaspoon freshly ground black pepper. Taste and adjust acidity or seasoning: add a little more lemon juice or vinegar if you want brighter acidity, or a pinch more salt.

Warm the potatoes (optional): If you prefer, rewarm the drained potatoes in a skillet over medium heat with a teaspoon of olive oil for 2–3 minutes, just until heated through and a few edges brown lightly. Otherwise use them at room temperature.

Toss and finish: Add the warm (or room-temperature) potatoes to the bowl with the dressing and gently toss to coat, being careful not to break the potatoes. Taste and adjust seasoning. Transfer to a serving dish and sprinkle the reserved bright green scallion slices on top for color and crunch.

Serve: Serve warm or at room temperature as a side dish. Leftovers keep refrigerated in an airtight container for up to 3 days; gently rewarm or serve chilled.