AHas anyone ever made the ihearteating.com choc whipped bc frosting recipe?

It's a choc version of heirloom frosting, which i love and have been filling my cakes with.

I made the following recipe (doubled it) and it WOULD NOTcome together. Just kept breaking and everytime I scraped the bowl, the scrapings were even more broken. Not sure if it was doubling, or maybe I didn't cook it long enough? It was pretty darn thick.

2/3 c unsweetened cocoa powder 1/4 c cornstarch 1 1/2 c milk 1 1/2 T vanilla 1 1/2 c butter at cool room temp 2 c gran sugar

(Now I did run my two cups gran sugar through my vitamix for a little to break it down...I can never seem to get through the grit otherwise. It wasn't powdered sugar consistency, but it was definitely smaller grains, but I still whipped it the prescribed amount of time)

Cook cocoa, CS and milk til thick. Cool. Add vanilla. Cream butter, sugar, salt. Add cooled mixture.

I said that if it looked separated to fridge for 1/2 hr and rebeat. I did that, but after that didn't work, I didn't have time to try it again. Threw it out and went with plan B. It basically turned to soup in my garbage can.

I really want to work on this because IT.WAS.DELICIOUS.

I don't know if it was because I doubled it, didn't cook it long enough? I am very willing to try again, but wanted any knowledgeable feedback from anyone who's tried it.

AAny baking wizzes out there that can take a look at this recipe?? Please...

It doesn't look too different from my recipe at home as far as ingredients... 

I actually put the sugar in with the milk while cooking though... and then if my icing ends up not stiff enough I add some powdered sugar to it... but I only use this icing for basic simple decorations...

Was your mixture cool before you added it to the butter?

AYes, it was cooled in the fridge overnight.

And that's a great idea to melt the sugar along with the milk! No problem with grains at all.

Does yours break down at all?

I want to use it as a filling, not icing, so not worried about piping it or anything.

Thanks for your help. Maybe I will try a single recipe this weekend.