Amounts are very approximate guesses (I don't usually measure the first time I make something from scratch). This is a good sauce paired with steak. It's a bit spicy, but you can tone back on the peppers.
Combine Chicken Stock, Brown Sugar, Ponzu, Soy, Peppercorn, Ginger, & Cocoa Powder in sauce pot over medium-high heat. (NOTE that Ponzu is a citrus soy sauce. Soy + drops of lemon juice can be substituted).
Whisk until well combined.
Bring to simmer, whisking frequently. The chocolate should be integrated into the liquid.
Combine Corn Starch and Water in a separate dish. Do not let settle.