In a saucepan over medium, add flour, corn starch, salt, cocoa, brown sugar. Whisk until mixed. Then make a well in the center. (Don’t let the pan get too hot during this process—keep on medium)
Add milk, one cup at a time. Whisk until it looks like chocolate milk. Wait till it comes to a simmer (light boil). You will start to see it thicken.
(While waiting for it to boil) In a seperate cup, whisk yolks together. With one of your used measuring cups, dip in the milk mix and whisk to incorporate into the yolk mix. This brings the yolks to a higher temperature without causing scrambled eggs.
Add yolk mix back into the chocolate mix, whisking while you pour.
Once it comes to a light boil, you will see it thicken. Your done! Now just remove from heat and let cool a little before you put it in the refrigerator. Refrigerate for at least 4 hours or overnight (preferably—then you can just assemble the next day).
Add to a trifle or put into little cups and add almond whipped cream when you are ready to serve. YUM.