Combine milk, cream, and half a cup of sugar into large pan on medium to medium-low heat, stirring occasionally to prevent sticking
In a separate, dry, clean bowl, whisk the egg yolks and remaining sugar until color is a light yellow and the mixture has begun to stiffen; continue watching the pan on the stove top
Once the stove top pan begins to simmer, reduce heat and add cocoa powder, vanilla, and chocolate; whisk briskly and allow chocolate to melt/combine thoroughly (about 5 minutes)
Slowly and carefully, add chocolate mixture into egg mixture while continuing to beat the eggs, ensuring they combine fully with each incremental pour, stir until color evens out; *this process may require the use of a heat-proof measuring cup or a friend
Pour combined mixture back into stove top pan and allow it to cook on low for 5-8 minutes, stirring occasionally, until the mixture reaches an internal temperature of 170° (160° is supposedly safe but going beyond a bit shouldn't hurt it)