Start by thoroughly rinsing your rainbow carrots under cool running water, using a soft vegetable brush to remove any soil. Don't peel them—the thin skin holds nutrients and adds beautiful color contrast. Pat them completely dry with paper towels; any moisture will create steam instead of char. Leave about 1-2 inches of the green tops attached (they'll darken beautifully in the oven and look rustic-elegant). If you have particularly thick carrots, cut them in half lengthwise so they cook evenly. You're aiming for pieces that are roughly uniform in thickness—about ½ inch thick—so they'll char simultaneously without some pieces burning while others remain undercooked. This is something I learned from watching professional chefs: uniformity in size is what separates restaurant-quality results from home cooking.

Place your prepared carrots in a large mixing bowl. Drizzle with 2 tablespoons of your olive oil and sprinkle with kosher salt, freshly cracked black pepper, and red pepper flakes. Use your hands to toss everything together thoroughly, making sure every carrot is evenly coated with oil and seasoning. This is crucial—uncoated spots won't char properly, and you want maximum contact with heat. Taste a tiny piece of raw carrot; it should taste lightly seasoned but not salty. The carrots will concentrate as they roast, so hold back if you're unsure.

Arrange your oven racks so you have clear space in the middle, then preheat your oven to 425°F. Allow at least 15 minutes for full preheating—this matters tremendously. While the oven heats, place a large sheet pan or cast iron skillet (if you have one) directly on the oven rack. Yes, put the pan in the oven while it preheats. This is the secret to achieving real char. The superhot pan is what creates those beautiful caramelized, slightly blackened edges that taste almost burnt but in the best possible way. When you're ready to roast (about 3 minutes before the oven finishes preheating), carefully remove the hot pan and arrange your oiled carrots in a single layer, cut-side down if you've halved any pieces. They should make a dramatic sizzling sound as they hit the hot pan. That sizzle is your confirmation that charring is about to happen.

Return the pan to the oven immediately. Roast for 20-25 minutes without stirring. I know this goes against every instinct to fuss with food, but don't open the oven door or stir the carrots during the first 15 minutes. The undisturbed heat is what creates the char. After 15 minutes, stir the carrots to ensure even cooking on all sides, then continue roasting for another 5-10 minutes until the carrots are deeply browned and tender when pierced with a fork. The thinner parts should have nearly black edges while the larger sections develop rich brown caramelization. This is exactly what you want—that contrast between sweetness and slight bitterness from the char is where the complexity lives.

About 10 minutes into the carrot roasting, prepare your herb oil so everything finishes around the same time. This is where you can work ahead beautifully. Add your basil, mint, shallot, garlic, and red pepper flakes to a food processor. Pulse until everything is finely chopped but not completely smooth—you want some texture. Don't over-process; you're looking for a rough pesto-like consistency. Pour in your olive oil and red wine vinegar, add salt and lemon zest if using, then pulse to combine. The oil should be bright green with flecks of herb throughout. Taste it and adjust: needs more salt? Needs more vinegar for brightness? This is your moment to balance it to your preference. Transfer to a bowl and set aside. The herb oil can be made up to 24 hours ahead; just store it covered in the refrigerator and let it come to room temperature before serving.

When the carrots emerge from the oven, they should be absolutely gorgeous—deeply caramelized, slightly charred at the edges, and completely tender. Transfer them to a serving platter, arranging them so the green tops and varied colors are visible. The carrots will be hot, so work carefully. Drizzle the fresh herb oil over the top, using about 3-4 tablespoons per serving (you likely won't use all the oil, which is fine—it keeps for a week refrigerated and is wonderful on grilled vegetables, fish, or pasta). Do this plating step just before serving, not ahead of time, so the herb oil stays vibrant and the carrots don't become overly saturated. Alternatively, you can serve the herb oil on the side in a small bowl so guests can control how much they want. This actually works beautifully for buffet-style entertaining.