Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.

In a large bowl, toss halved baby potatoes with 2 tbsp olive oil, 0.5 tsp salt, and 0.25 tsp black pepper until evenly coated.

Spread potatoes in a single layer on the prepared baking sheet. Roast for 20 minutes, flipping halfway through, until golden and tender.

While potatoes roast, prepare the dressing: whisk together lemon juice, Dijon mustard, 2 tbsp olive oil, minced garlic, 0.25 tsp salt, and 0.125 tsp black pepper in a small bowl.

Transfer roasted potatoes to a large serving bowl. Pour dressing over warm potatoes and toss gently to coat.

Let cool for 5–10 minutes. Garnish with chopped parsley and chives if desired. Serve warm or at room temperature.