Slice tomatoes in half and place on a baking tray. Roughly chop the serrano pepper, garlic, and onion. Toss with 1 tablespoon of olive oil and sprinkle over tomatoes. Place in over and roast until everything is soft and lightly browning, 45-55 minutes.
Remove corn from cob. Easiest way to do this is remove husk and place perpendicular in a large bowl, carefully cutting downwards. Toss with remaning tablespoon of olive oil and place on a separate baking tray. Roast until lightly browning, 15-20 minutes.
In a food processor, combine roasted tomato mixture and cilantro. Pulse until combined. Squeeze in lime juice and salt, pulsing a few more times. Remove, place in a bowl, and stir in roasted corn.