Preheat the oven to 180 degrees C / 375 F.
Add the caster sugar and continue to beat until it forms stiff peaks and it’s has a shiny meringue-like consistency.
No need to use a mixer from now on, a silicone spatula would do just fine.
In go the flour, oil, cocoa powder, baking powder and vanilla extract.
Bake for about 10 minutes until the sponge is well risen.
Pour the double cream in a pan and place on a low heat.
For the chocolate glaze, combine all ingredients together, then leave to cool.
Spread the chocolate cream over the sponge, leaving about 1-2 cm around the edges, then carefully roll into a big sausage.