A birthday girl needs cake

Today is a friend's birthday. This is good news for her but it's also good news for me. I now have an excuse to try my first recipe from 'Bake & Decorate' by Fiona Cairns. I've had this cookbook for a few weeks but in an attempt to be virtuous for the month of January, I've been studiously avoiding the temptation of the recipes contained inside.

This is coming to an end right now because I'm going to bake this cake, a flourless chocolate hazelnut cake:

This cake ticks all of my boxes.
Chocolate?
Yes.
Gooey, moist chocolate?
Yes, yes, yes.
Gooey, moist chocolate with chocolate ganache and raspberries?
Yes, yes, yes, yes, YES...!

Here's the recipe:
Ingredients for the cake:
90g unsalted butter, cubed
60g blanched hazelnuts
150g chocolate, 70% cocoa solids, broken into pieces
90g golden caster sugar
3 eggs, separated

Ingredients for the ganache:
100g chocolate, 70% solids, broken into pieces
50ml double cream
25g unsalted butter
400g raspberries

• Preheat the oven to 180 degrees.
• Butter a 20cm round cake tin and line the base with baking parchment.
• Roast the hazelnuts in the oven for 5 mins or so. (Watch carefully to make sure they don't burn.)
• Cool the hazelnuts and grind finely in a food processor.
• Place the chocolate, 70g of the sugar and the butter in a bowl over gently simmering water (make sure the bowl is not touching the water) and melt together very gently.

• Remove from the heat and stir in the hazelnuts.
• Beat the egg yolks together until they change to a paler colour, something like this:
  

• Then add them to the cooled chocolate mixture.
• In another (very clean) bowel, whisk the egg whites and then slowly add the remaining caster sugar until the mixture forms soft peaks.
• Take a large spoonful and fold it into the chocolate mixture to lighten it a little.
• Then fold in all of the remaining egg whites as gently and as lightly as you can, using either a large metal spoon or a spatula.
• Pour into the tin and bake for 20 mins.
• Leave to cool for 15 mins then run a knife around the edges to loosen it from the tin.
• When the cake is cool, turn it very carefully out onto a serving plate, using the base as the top.
  
• To make the ganache, melt the chocolate, cream and butter in a bowl over very gently simmering water (again making sure it doesn't touch the water). Stir together and then cool a little until it thickens.
• Pour over the cake and spread with a palette knife.
• Stud the surface with raspberries and you should have something that looks like this:

Yum! Now to deliver it to the birthday girl...

(This cake is very easy to make. It's ready in next to no time. The fact that it's flourless means that it's suitable for people on gluten-free diets. I'll definitely be making more from this cookbook.)

Addendum: In fact, I liked this cake so much that I made it for my boyfriend within 24 hours of delivering it to the birthday girl. This time, I omitted the butter from the ganache and I thought it worked better. I don't know if anyone else finds this but every time I make ganache with butter in it, the butter separates and forms a not-very-attractive film on top. Anyone got any ideas why this might be?