For the spicy peanut sauce: Combine the peanut butter, soy sauce, oil, vinegar, brown sugar, garlic, ginger, chili paste and water in a blender. Blend until smooth, adding more water as needed. Set aside.
For the wontons: In a large bowl, combine the pork, shrimp, chives, sesame oil, soy sauce, brown sugar, salt and pepper. Mix everything gently but thoroughly together with your hands (or a wooden spoon).
Bring a large saucepan filled with 3 to 4 inches of chicken stock to a boil.
Place 1 tablespoon of the pork mixture in the middle of a wonton wrapper. With your finger, dab the edges of the top half of the wrapper with beaten egg. Fold the top over to enclose the filling, press to seal the edges, then fold two corners in and press to seal the corners together. Place the finished wonton on a lightly floured baking sheet and repeat with the rest of the filling and wrappers.
When you have enough wontons to begin to cook, gently transfer wontons into the boiling stock, making sure not to overcrowd the pot. Simmer until the filling is cooked through, about 5 minutes. Continue forming wontons while the batches cook.
Transfer cooked wontons to a bowl. Top with peanut sauce, a drizzle of toasted sesame oil, and garnish with some cilantro and serrano pepper slices. Enjoy!
Any uncooked wontons can be stored in the fridge on a plate covered with plastic wrap for up to 1 day or frozen for 3 months.