Biscuit Sponge
This isn't a description of a sponge I'd come across before, though I understand it now...in many ways it's similar to a genoise sponge, but with a lot more dry ingredients. It's certainly a lot of eggs! (4 eggs and 5 egg whites...the yolks are sitting in the fridge in a ramekin of water, waiting to be turned into custard). I was concerned that folding the egg and nut mixture into the meringue was going to be tricky, but they actually went together OK, and I was able to keep a reasonable amount of air in them.
Once it's baked and cooled, it's actually fairly firm (hence where I think the "biscuit" descriptor comes from...that or I over-baked it!), and quite easy to cut. It also took on the soaking syrup fairly well...again I was concerned that this would run off the surface (concerned enough that I put some fork holes across each slice), but it went in OK.
I'd love to find somewhere that sells ground pistachio (or pistachio flour, as it's apparently also known). I make it by whizzing pistachio kernels in a food processor, but it's not as fine and consistent as I'd like...good if you want texture, but not it you want a well-crumbed cake.
Soaking Syrup
I made a slight mistake here, and added the orange juice before I boiled the mixture...not sure what impact this would have had. otherwise it has the nice acidic citrus flavours you want. I would say the cardamon did not come through as strongly as I expected. I used the juice from 2 medium oranges (which I'd zested for the buttercream), and kept a small amount of the juice aside for the buttercream as well
Chocolate Ganache
This was a slightly different way of making ganache to anything I've done before...using hot milk to melt the chocolate, and then adding in butter afterwards, and it worked really well! It's much easier working with milk in a saucepan, and it melted the chocolate far better. I possibly let it cool a little too much before assembly.
Orange Buttercream
This was a surprisingly basic buttercream (I now half-expect everything to use meringue bases, or egg yolks)...simply butter and orange zest whipped together, then sugar and orange juice added in. The recipe says to whip it for a long time, and it's definitely one where a stand mixer rescues you.
Mirror Glaze
I was really pleased to find this recipe on the website...it's something I've been wanting to try for ages, as it's a great presentation skill. It uses a lot of cocoa powder, and it's also very adhesive (when I was trimming the cake, the glaze would stick to anything it touched). I think I put it onto the cake a little too cool, and it didn't quite run enough, though I have the lovely shiny finish still, after levelling it with a palette knife. Next time I may give it 10 seconds in the microwave to make it a bit runnier. I really like that it can be prepared ahead, and re-heated.Assembly
I think the key tip here is the use of a hot knife to get nice, clean edges to the cake. This is almost certainly the neatest cutting I've done, and with the layers of this cake, that's really important. I'll admit to skipping a couple of the chilling stages, as the cake was fairly firm and stable as I built it up. I chilled it before topping off with the ganache (which I did a lot of smoothing on, to try and keep the cake as square as possible), and before applying the mirror glaze, and then again before trimming the edges. The cake was in the fridge overnight before I sliced it up (again with a hot knife).