Start by positioning your oven rack to the middle position and preheating to 400 degrees Fahrenheit. This temperature is the sweet spot—hot enough to create caramelization and char edges, but not so intense that everything burns before it softens. While the oven warms, prep your ingredients. Rinse your tomatoes and pat them dry. Slice your habaneros in half lengthwise, then use a small spoon to remove the seeds and white veins inside—this is where most of the intense heat lives. (I keep my hands away from my face while doing this. If you want to be extra careful, wear disposable gloves.) Peel your half onion and cut it into roughly four equal quarters. Leave your garlic clove unpeeled; it'll roast whole and soften beautifully. Cut your fresh mango into roughly 1-inch cubes. You want pieces substantial enough that they won't disappear during roasting but small enough that they'll roast evenly.

Place your sheet pan on the counter and arrange your tomatoes, habanero halves, onion quarters, mango cubes, and whole garlic clove on it. Try to space them out so they're not crowded—this helps them roast rather than steam. If you're using olive oil, lightly brush or mist the pan and ingredients. I typically use about a tablespoon total, just enough to help with browning and prevent sticking. Season everything lightly with your kosher salt.

Place your sheet pan in the preheated oven and set a timer for 30 minutes. You're looking for the edges of the tomatoes to darken (not blacken completely, but definitely caramelized), the mango to take on golden-brown patches, the onion to soften and char slightly at the edges, and the garlic to feel soft when you press it gently. Don't stir or fuss with anything during this time. Let the oven work its magic. The hands-off approach is what creates those beautiful caramelized flavors. At around the 20-minute mark, if things seem to be browning faster than softening, you can give the pan a quarter turn or loosely cover it with foil, but this is rarely necessary. You'll know it's ready when the tomato edges look blistered and darkened, the mango's surface shows golden-brown patches, and the garlic feels completely tender. If you poke the tomatoes, they should yield easily to pressure.

Remove your sheet pan from the oven and let everything cool for about 5 to 10 minutes until it's cool enough to handle. Once it's cooled slightly, pop that roasted garlic clove out of its papery skin—the flesh inside should be soft and creamy. Discard the skin. This resting period also helps the flavors set slightly and prevents the finished salsa from being too hot when you blend it, which actually helps preserve the brightness of the cilantro you'll add next.

Transfer all your roasted ingredients to a food processor or high-speed blender. Add your lime juice, the optional cumin, and most of your cilantro (save a small handful for garnish, which sounds fancy but honestly just makes it look beautiful). Pulse or blend until you reach your preferred consistency. I like mine slightly chunky—you can still see pieces of mango and tomato—rather than completely smooth. This gives the salsa texture and makes it more visually appealing. If you prefer silkier texture, blend longer. If you like it chunkier, pulse fewer times. Taste as you go. Add your salt gradually, tasting between additions, until it hits that perfect balance where the sweetness of the mango and the heat of the habanero are both prominent but neither overwhelms the other.

Fold in your remaining fresh cilantro by hand after blending. This preserves its brightness and prevents it from becoming bitter from the heat of the blender. Taste one final time and adjust salt or lime juice if needed. Transfer to a serving bowl and if you're serving it right away, you're done. If you're making it ahead (which I highly recommend), cover and refrigerate until serving time.