1. Preheat the oven to 350°. Cut off the top third of the garlic heads. Stand them cut side up on foil and drizzle with 1 teaspoon of oil. Wrap the garlic in the foil and bake for about 1 hour, until very soft. Squeeze the garlic into a bowl. Stir in the lemon zest, butter, cilantro, tarragon and the remaining 1 tablespoon of oil. Season with salt and pepper.
2. Light a grill. Peel back the corn husks, keeping them attached. Discard the silk. Spread the herbed garlic all over the corn. Fold the husks back over the corn and tie the tops with string. Wrap the corn in foil.
3. Grill the corn over moderate heat, turning, until the kernels feel tender, 15 minutes. Remove the foil. Grill the ears over moderately high heat, turning, until the husks are nicely charred, 5 minutes, then serve.