Hi, I’m trying to replicate this so I have a hot chocolate beverage available that is also keto-friendly.
I don’t want it to be too expensive, so I would only use 3 ingredients:
What ratio of erythritol to cocoa would you recommend? In grams please.
Also, would erythritol properly melt with boiled water?
I don’t know the answers to your questions but I would suggest using a combination of nut milks and heavy cream rather than water. Non keto hot chocolate recipes usually call for powdered milk so I think in water it will be lacking.
Maybe: http://a.co/gmxXmm6 (splenda)
or: http://a.co/hsgeXT8 (monkfruit)
I don’t live in a country amenable to cost effective Amazon orders, hence the replication effort.
Hm, powdered milk has 38g of carbs to 100g, and cocoa powder has 24g of carbs to 100g. So, all together they would come to your regular sugared product, be it chocolate or coffee.
When I make keto hot chocolate I don’t use any sweetener at all and it’s divine. But, maybe it’s the booze. 
~1/2 to 2/3 c. heavy cream or half and half
~1/2 c. hot water
2-3 TBLS Hershey’s Unsweetened cocoa
splash of vanilla extract
2 oz. Jameson
Warm cream on stove top. Add cocoa powder and whisk until completely blended. When the cream is as hot as you want it, pour into mug and add 1/2 cup hot water, vanilla and Jameson. Top with home made whipped cream if you have any!
This is a pretty heavy duty beverage, so on the rare occasion when I drink it, I do so with the understanding it will affect my weight loss progress. But, when it’s cold and blustery outside it’s totally worth it!
Fairly complicated task to get there with water. If you are building from a dairy product, then you can go pretty easily with a sweetener of your choice and a cocoa powder of your choice, or with a bit more stirring, just a chocolate bar of your choice.
I use unsweetened vanilla almond milk (1 cup has 30 cal, 1g carb), cocoa powder, and either monk fruit or erythritol. Also, if you add a little almond or vanilla extract (or sometimes mint), it helps. 
It’s extremely low calorie. If you want additional fat, add in some coconut oil (or butter or MCT) and blend!
I buy Lakanto chocolate drink mix as well, but if you don’t have access to that (also it’s expensive), this should work.
I just tried to make it with cocoa powder, steaming water and vanilla extract.
It was good, but I think adding powdered milk in 1:1 ratio to cocoa powder would be the key ingredient for the real hot chocolate experience.
My keto hot choc is simple.
boil kettle
add cocoa (approx 2 teasp) to a mug
mix into a paste with double (heavy) cream (approx a couple of tablespoons)
add boiled water to the top
stir
sweeten to taste with sweetener of choice, or mint or caramel zero carb essences
All quantities are variable and adjustable for personal preference, so it is impossible to give quantitites in grams.
I think this might be the key to keto chocolate, just adding that + the cocoa powder. 6g+6g of both for one mug of hot chocolate.
The carbs would be negligible.
Adding fat does not reduce carbs.
Bulletproof Hot Choc…
Unless made unsweet, as say Mayan xocōlātl beverage, any hot choc will require a sweetener for the popular western taste. I assume you mean a SF version, but want to be clear that you cannot take a packet of normal swiss miss and make it keto by adding coconut oil. Not saying you don’t know this, but as this is a public portion of the forum, and similar questions have been asked for the history of LCHF on the internet, want to be clear.
It has 20g of carb per 100g. You might as well add milk!
I add cream and swerve to powdered cocoa
Ah… i think this is one of those transatlantic translation things. 
Here in the UK ‘cocoa’ is pure unadulterated cocoa powder, with no added milk powder, sugar or flavourings.
We do have pre-mixed hot choc powders (which I haven’t bought in years) but that is usually known as ‘hot chocolate’. So i would expect to buy ‘cocoa’ for cooking, or to make my own hot cocoa/choc drink by adding my own cream and sweetener, or i could buy ‘hot chocolate’ in powder form which is already a blend of milk, cocoa powder and gawd knows what other carbage.
That was probably far more info than you wanted or needed, but at least it explains my query.
Similar in the US there is Hersheys or other powder which is usually in a tub and states unsweetened on it which you might use for baking. Then there is Hot Cocoa or Hot Chocolate which can be in a tub or packets and generally those would have added ingredients such as milk and sweetner but you always need to check