Thick Film when Boiling Milk

What is it--and why is it???
When I make homemade hot chocolate (milk + cocoa + cane sugar + vanilla extract), I have to skim off a bunch of (to me, kind of gross) stuff that only happens when I am heating milk. Please enlighten me as to what this is and why it happens?

To avoid, I don’t heat the milk to boiling.

I feel John is on the right track.  Don't boil the milk.

Get the milk warm then add the other ingredients slowly.

To help blend in the powdered cocoa add a little water and make a paste.

It is called hot chocolate, not boiled chocolate.

From Wikipedia: https://en.wikipedia.org/wiki/Milk_skin

Milk skin or lactoderm refers to a sticky film of protein that forms on top of dairy milk and foods containing dairy milk (such as hot chocolate and some soups). Milk film can be produced both through conventional boiling and by microwaving the liquid, and as such can often be observed when heating milk for use in drinks such as drinking chocolate. It is caused by the denaturation of proteins such as beta-lactoglobulin (whey protein). The thickness of the skin varies dependent on a number of factors, including the temperature of the milk, the shape of the container, and the amount of milk in the container.

When milk is boiled, soluble milk proteins are denatured and then coagulate with milk's fat and form a sticky film across the top of the liquid, which then dries by evaporation. The layer does not need to be discarded and can be consumed, as protein's nutritional value is unaffected by the denaturation process. Milk film is often considered to be desirable and is used in several recipes for various foods. However, this is dependent on culture. For example, French Psychoanalyist Julia Kristeva's influential account of the abject uses the skin on milk as an important example of Horror.

i get it when i heat milk (not boil) to make yogurt. It seems to appear after you pass 150F (I stop at 170, don't even get close to boiling).
Here people call it the cream, but it's... not cream. Doctor google says it's fat and protein. I kind of like eating it, like the skin on pudding (yes, i'm a monster).

you may find this interesting, if not particularly enlightening. https://cooking.stackexchange.com/questions/8803/why-and-when-does-a-skin-form-on-heated-milk-and-how-can-i-prevent-it