Dice the red onion finely and set aside. Seed and dice the jalapeños, removing the white pith to control heat level. Chop the fresh cilantro and set aside. Cut the tomatoes into quarters, then roughly chop them into bite-sized pieces. Measure out the lime juice, salt, pepper, and cumin into small bowls for easy access during assembly.

Heat your grill to medium-high heat. Lightly oil the corn and the whole jalapeños to prevent sticking. Place them directly on the grill grates and cook for 5-10 minutes, turning occasionally, until the corn kernels are charred in spots and the jalapeños are blistered and softened. The char adds deep, smoky flavor that's essential to this salsa. I prefer to let the corn get fairly dark—those blackened bits are where the real flavor is.

Transfer the jalapeños to a bowl and cover tightly with plastic wrap or a lid to trap steam, which helps loosen the charred skin. Let them sit for about 5 minutes. Meanwhile, place the corn on a cutting board to cool. Once the jalapeños have cooled slightly, peel away the charred skin with your fingers or a knife—it should come off easily. Cut the jalapeños in half lengthwise and remove any remaining seeds for a milder salsa, or leave some seeds if you prefer more heat.

Hold each ear of corn upright on a cutting board and use a sharp knife to slice the kernels off the cob in downward strokes, rotating as you go. In a large mixing bowl, combine the corn kernels, diced jalapeños from Step 3, and the chopped tomatoes and red onion from Step 1. I like to add the tomatoes last since their juice will start breaking down the other vegetables if they sit too long.

Pour the lime juice over the vegetables and add the salt, pepper, and cumin. Gently fold everything together until well combined, being careful not to crush the corn kernels too much. Taste and adjust seasoning as needed—salsa often benefits from a little extra lime juice or salt to brighten the flavors. Fold in the fresh cilantro last so it stays vibrant and fresh.