How to Make It
Preheat the broiler and position a rack 8 inches from the heat. Broil the bell peppers and jalapeños until blackened all over. Transfer to a bowl and cover with plastic wrap for 20 minutes to loosen the skins. Peel the bell peppers and jalapeños, then remove the seeds and ribs and transfer to a food processor. Pulse until finely chopped but not pureed, then scrape into a bowl.
In a saucepan of lightly salted boiling water, blanch the corn for 1 minute. Drain and let cool.
In a small dry skillet, toast the fennel and cumin seeds over moderately high heat, shaking the pan frequently, until fragrant, 2 to 3 minutes. In a spice grinder, grind the seeds to a fine powder. Add the corn, lemon juice, basil and the ground seeds to the bowl. Season the salsa with salt and black pepper and let stand for 2 hours.