Step 1: Prepare your aromatics by finely mincing the fresh garlic cloves and grating the fresh ginger. Set aside.
Step 2: In a medium bowl, whisk together the soy sauce, rice vinegar, hoisin sauce, granulated sugar, brown sugar, grated fresh ginger, minced fresh garlic, red pepper flakes, and sesame oil. Whisk until both sugars are fully dissolved.
Step 3: In a separate small bowl, create a cornstarch slurry by whisking together the cornstarch and cold water or chicken broth until smooth and no lumps remain.
Step 4: Heat a small saucepan or wok over medium heat. Pour in the whisked sauce mixture from Step 2. Bring the sauce to a gentle simmer, stirring constantly.
Step 5: Once the sauce is simmering, slowly pour in the cornstarch slurry from Step 3 while continuously whisking. Continue to whisk for 1-2 minutes, or until the sauce thickens to your desired consistency, enough to coat the back of a spoon.
Step 6: Remove the sauce from the heat. Taste and adjust seasonings as needed. If you prefer more heat, add additional red pepper flakes. If you like it sweeter, stir in a pinch more sugar. Serve warm over your favorite protein or vegetables.