While it's still hot, pour the Creme Anglaise/gelatin mixture over the chocolate and cover the bowl with a dish to hold the heat. Wait at least 45 seconds (or longer) for the chocolate to soften. If you're not sure you've completely dissolved the gelatin or if you've (heaven forbid!) partially cooked the eggs, you can strain the mixture as you pour it in.
Starting in the middle with a whisk, swirl the chocolate and egg/milk/gelatin mixture. At first it will look like chocolate milk, but in no time you'll have a silky ganache.
Retreive your mixing bowl and whisk from the refrigerator and add the 1.75 C of cold heavy cream to the bowl along with the powdered sugar and corn starch (if using)
Whip the cream to SOFT peaks. Do not over-mix. Soft peaks means that they form and instantly slump when you pull the whisk from the mixture. At medium-high speed on stand mixer, this shouldn't take more than two minutes and probably less.
By this time the temperature of the chocolate mixture should have reduced to roughly body temperature. It's ok for it to be warm, but if you let it cool too long or let the gelatin set up, it won't mix properly. If necessary, you can warm it for a few seconds in the microwave. Add one third of the whipped cream to the chocolate mixture and gently fold it in.
Add the resulting cream/chocolate mixture to the big bowl with the rest of the whipped cream and gently fold it in until no streaks show. Be gentle--don't collapse the air you just whipped into the cream!
You're not done yet! It will have a pudding-like texture at this point, and it needs to chill at least an hour or, preferably, overnight, in the refrigerator before you can use it on your cake. (If you're not making a cake but, say, a Parfait, then you can spoon it into molds or cups at this point, but the texture won't be mousse-like until it cools.