Chocolate and Hazelnut Bars

This recipe has been adapted from the one given by Rachel Allen in her recent book. I found it on the BBc web site. I've made some changes as I thought that her recipe was too sweet so here is my version.

For the chocolate base:
200g/7oz butter
50g/2oz cocoa powder
200g/7oz caster sugar
2 free range eggs, beaten
225g/8oz plain flour
For the hazelnut caramel layer
125g/4½oz butter
1 x 397g/14oz tin condensed milk
2 tbsp golden syrup
75g/3oz caster sugar
125g/4½oz toasted and halved hazelnuts
For the chocolate topping
200g/7oz dark chocolate, chopped
1 tbsp sunflower or vegetable oil

Method
1. Preheat the oven to 160C/325F/Gas 3 and line the base of or grease, a small Swiss roll tin measuring 20x30cm/8x12in.
2. In a medium sized saucepan over a medium heat, heat the butter for the chocolate base, stir in the cocoa powder and then the sugar and mix until smooth.
3. Remove from the heat and stir in the eggs until mixed and then the plain flour.
4. Spread the chocolate base over the prepared tin and bake in the oven for 20 minutes until firm on top.
5. Remove from the oven and set aside to cool while you make the hazelnut caramel layer.
6. In a medium-sized saucepan over a medium heat, melt the butter and then add the condensed milk, golden syrup and sugar.
Turn the heat to low and stir continuously for 12-15 minutes until the mixture is dark caramel in colour (do not let it burn).
7. Remove from the heat and stir in the nuts. Spread evenly over the chocolate base and allow to cool.
8. Melt the chocolate in a bowl sitting over a saucepan of simmering water. When it is melted, stir in the oil and then pour over the caramel layer and smooth out, leaving to cool and set.
9. To serve, cut into squares. These will keep for a week in an airtight container.