Preheat a convection/fan-assisted oven to 350°F (180°C) and line a large baking sheet with parchment paper.
Peel the carrots and cut them into similar-size pieces so they roast evenly. Small, thin carrots can be left whole.
In a large bowl, whisk together the melted butter, olive oil, maple syrup, and honey. Add the chopped garlic, leaves from 2 sprigs of thyme, salt, and black pepper.
Add the carrots and toss until they’re thoroughly coated in the glaze.
Spread the carrots over the prepared baking sheet in a single layer, making sure they aren’t overlapping. Pour any glaze left in the bowl over the carrots and add another 2–3 thyme sprigs on top.
Roast for 25–30 minutes, turning the carrots halfway through, until they’re tender and lightly caramelized around the edges.
Remove the carrots from the oven. Pour the lemon juice over them and toss gently.
Transfer to a serving platter and finish with chopped parsley and fresh thyme leaves.
For a little more sweetness, drizzle with extra maple syrup or honey just before serving.