In a medium saucepan, whisk together all sauce base ingredients: soy sauce, brown sugar, rice vinegar, sesame oil, minced garlic, grated ginger, gochujang, and black pepper.
If using, stir in optional honey and red pepper flakes.
Place the saucepan over medium heat. Bring the mixture to a simmer, stirring occasionally.
Once simmering, reduce the heat to low and let it cook for 10-15 minutes, stirring occasionally, until the sauce has thickened slightly. It should coat the back of a spoon.
Remove from heat and let it cool slightly before using.
Notes
This sauce can be stored in an airtight container in the refrigerator for up to 2 weeks. Adjust sweetness and spice to your preference.