I would recommend Pierre Hermes' technique when making a curd.
Zoe's method is the old way of doing things in which the butter is cooked with the mixture. this separates the butter and produces a greasy final product.
Pierre Hermes cooks the sugar, fruit juice, and eggs first, then emulsifies the butter into the mixture after cooking and cooling some.
This produces a smooth and creamy bright filling that is far superior to the cooked butter curds and fillings.
Artificially thickened curds (cornstarch or gelatin) have a terrible texture. Since they are gooey and thick they have a very unpleasant mouth-feel.
Bon Appétit did a version of Pierre Hermes’ curd with mangoes. Smitten Kitchen blog posted a version of the Bon Appétit version. She hand whips the butter into the mixture. But it is normally done with a food processor.
I wrote a post on lemon curd using Hermès’ recipe and technique. And there are other explanations of the technique online.
The key is cooking the mixture to the correct temperature. The technique produces such a superior filling it's pretty much the standard among pastry chefs.
Regarding ganache…
Two important aspects of ganache:
1. Using Heavy cream, 35% milkfat. Regular cream does not have enough milkfat at around 30%.
2. The ratio of couverture chocolate to heavy cream. Yes, the chocolate should be couverture.
Ganache ratios
Glaze: pourable 1:2
- Chocolate 100%
- Heavy cream 200%
Ganache for Filling: 1:1
- Chocolate 100%
- Heavy cream 100%
Whipped ganache (truffles, fillings, etc) 2:1
- Chocolate 100%
- Heavy cream 50%
When layering fillings in a shell use a pastry bag fitted with a piping tip no more than 1/2”. Even layers create a pleasant aesthetic when sliced and plated, and more importantly, an even surface is necessary when glazing. Just be beware with pastry cream under a glaze you’re not going to have the best-looking results.
Chill the bottom layer completely before piping on the next layer of filling.
You’ll need to place plastic wrap on the surface of the curd and pastry cream when chilling otherwise it will form a skin.
For pastry cream recipe see pastry chef Eddy Van Damn. I wouldn’t use gelatin to set a pastry cream as it will create a glue like texture.
How to make perfect eclairs or choux paste without big cracks.
chefeddy.com
If you want to make a chocolate glaze using cocoa powder
Chocolate Glaze:
6g gelatin (in sheet form)
40g water
120g sugar
40g unsweetened cocoa powder, sifted
80g whipping cream (min 35% fat)
Instructions:
Put gelatin into large bowl of cold water.
Over medium heat, stir sugar and water until dissolved then bring to boil.
Pour it over cocoa powder and stir until combined.
Put cream into saucepan over heat. As soon as comes to a simmer, remove from heat, squeeze excess water out of gelatin and add into cream. Stir until dissolves completely.
Pour cream over chocolate mixture and stir until combined.
Mix with electric hand blender.
Strain through sieve.
Cover with clingfilm and refrigerate 2 hrs (or can make up to 4 days in advance and store in fridge).
Remove from fridge, stir, smooth out any lumps then leave to sit at room temp. (or if made more than 2 hours in advance and the gelatin has set, warm in a pan over low heat until just melted then leave to come to room temperature).
