Preheat the oven to 160°C, fan forced, or 180°C conventional. Line and grease a 20cm springform pan with parchment paper.
In a heatproof dish, melt the butter and dark chocolate together until just melted. I prefer using the microwave, but you can also do this in a water bath. Use a rubber spatula to stir the mixture every few seconds to prevent it from seizing. Set aside to cool slightly.
To roast the almonds, heat a dry, heavy-based skillet over high heat. Add the raw almonds and toss continuously until golden and roasted. You want to really push them and get good color all around - this is where the rich, nutty flavor develops. However, be sure not to burn the almonds - keep moving them around in the skillet. Remove from the pan and set aside to cool.
In a stand mixer, or electric hand mixer, whisk together the eggs and sugar until doubled in volume, fluffy, and pale yellow.