Grease and line 3x7 inch baking tins with greaseproof paper. Preheat the oven to 160 degrees celsius. (fan)
Whisk the eggs and sugar together until pale and fluffy using and electric whisk or free standing mixer.
Add the oil to the mix and continue to whisk.
Pour the hot water over the chocolate and mix together.
Sieve together the flour, cocoa powder, baking powder and salt. Mix together the buttermilk and vanilla.
Add the chocolate mix to the eggs. Mix until well incorporated.
Alternatively, add the dry ingredients and buttermilk into the mix, whisking after each addition. Mix until well incorporated.
Divide equally between the three tins. Place in the oven and bake for 30-45 minutes. Until when an inserted skewer comes out clean. Leave to cool completely.