1. Roast jalapenos over gas flame or under broiler, until blackened, turning as needed. Transfer to small bowl, cover tightly with plastic, and let steam until cool enough to handle, about 15 minutes. Peel, seed, and remove stems from peppers. Reserve any liquid that has collected in bowl. Cut peppers lengthwise into 1/8-inch-thick strips. Set aside.

2. Set aside one tomatillo; blanch the rest in boiling, salted water, 3 minutes. Drain; place under cold running water to stop cooking.

3. Transfer half the tomatillos to blender. Add garlic, 1 cup cilantro leaves and stems, lime juice, salt, and pepper. Blend until smooth. Add remaining tomatillos, and blend until smooth. Transfer to a medium bowl.

4. Cut serranos into 1/8-inch dice. Stir into tomatillo mixture with 6 cilantro leaves, reserved pepper strips, and any collected juice.

5. To serve, cut reserved tomatillo into 1/4-inch-thick slices. Grill on greased grill pan or in skillet. Arrange slices over salsa. Slice avocado thinly. Sprinkle salsa with remaining 6 cilantro leaves, and top with avocado.