For the peanut sauce:
3/4 cup natural-style creamy peanut butter
1/3 cup water
3 tablespoons hoisin sauce
2 tablespoons freshly squeezed lime juice (from about 1 1/2 medium limes)
4 1/2 teaspoons soy sauce
1 tablespoon granulated sugar
2 1/4 teaspoons chile-garlic paste
1 medium garlic clove, mashed to a paste
1/2 teaspoon toasted sesame oil

For the summer rolls:
24 medium shrimp (about 1 pound), peeled and deveined (or use firm tofu)
4 ounces dried rice stick noodles or rice vermicelli
16 (8-1/2-inch) round rice paper wrappers
1 cup mung bean sprouts (about 3 ounces)
32 medium fresh mint leaves (from about 1 bunch)
32 fresh basil or Thai basil leaves
16 small fresh cilantro sprigs
2 serrano chiles, stemmed, halved, seeds removed, and thinly sliced lengthwise into 32 pieces (optional)
1 medium English cucumber, peeled and cut into 1/4-by-1/4-by-2-1/2-inch sticks
3 medium scallions, quartered lengthwise, then cut crosswise into 2-1/2-inch pieces (white and light green parts only)
8 Bibb lettuce leaves, cut in half