Preheat the oven to 425°F (220°C). Line a rimmed baking sheet with parchment paper or lightly oil it. Trim carrot tops and peel the carrots. If carrots are large, cut them lengthwise into halves or quarters so pieces are roughly the same thickness (about 1/2 inch) for even cooking; leave small carrots whole.

Toss with oil and seasonings

Place the prepared carrots in a large bowl. Add 2 tablespoons olive oil, 1 teaspoon honey, 1 tablespoon fresh thyme leaves, 1 minced garlic clove, 1 teaspoon sea salt, and 1/2 teaspoon black pepper. Toss thoroughly so each carrot piece is evenly coated. If using butter, cut into small pieces and add now so it can melt over the hot carrots while roasting (or reserve to finish).

Arrange and roast

Spread the carrots in a single layer on the prepared baking sheet with the cut side down if applicable. Avoid overcrowding so carrots roast rather than steam. Roast in the preheated oven for 20–25 minutes, turning once about halfway through, until carrots are tender and caramelized at the edges. Thicker pieces may take up to 30 minutes; test with a fork for tenderness.

Finish and garnish

Remove the carrots from the oven. If you reserved the butter, add it now and toss so it melts and glazes the carrots. Taste and adjust seasoning with additional salt or pepper if needed. Sprinkle 1/2 teaspoon lemon zest and 1 tablespoon chopped parsley over the carrots for brightness and color. Serve warm.