In a small saucepan, combine the soy sauce, peanut butter, honey or molasses, rice vinegar, minced garlic, sesame oil, Chinese five-spice powder, and red pepper flakes (if using).
Heat the mixture over medium-low heat, stirring constantly until the peanut butter melts and the ingredients are well combined.
Remove the saucepan from the heat once the sauce is smooth and heated.
Taste the hoisin sauce and adjust the seasoning if needed, adding more soy sauce for saltiness, honey for sweetness, or red pepper flakes for he
If you prefer a thinner consistency, you can stir in a tablespoon of water until you reach your desired thickness.
Transfer the hoisin sauce to a serving bowl or a clean jar with a tight-fitting lid.
Let the sauce cool to room temperature before serving.
Use the hoisin sauce as a dipping sauce for spring rolls and dumplings or as a condiment for stir-fries, grilled meats, or roasted vegetables.