Preheat the oven: Preheat the oven to 356°F/180°C (320°/160°C fan)
Prepare the baking pans: Grease and line two 8 inch (20cm) round baking tins with parchment or baking paper.
Chop the chocolate into chunks: If you are using a slab of chocolate, then roughly chop it up into little pieces or chunks. Add one teaspoon of flour to the chopped chocolate pieces or chocolate chips. Transfer the chocolate chunks or chocolate chips to a bowl and toss it in one teaspoon of cake flour until they are well coated, set aside. See note 4
Cream the butter and sugar: Use a large bowl to cream together the butter and sugar. Beat for 2 minutes until the mixture is pale in colour and has a light and fluffy texture.
Whisk together the wet ingredients: In a separate bowl, whisk together the following wet ingredients (eggs, yogurt and vanilla extract).
Add creamed butter mixture to wet ingredients:Gradually add the creamed butter mixture to the whisked egg mixture.
Sift in the dry ingredients: Sift in the flour, baking powder and baking soda (bicarbonate of soda) folding in with a spatula to combine.
Fold the chocolate into the batter: Add in the flour-coated chocolate chips or chunks and mix into the batter until evenly distributed.
Transfer batter to cake tins: Divide the cake batter between the prepared cake tins.
Level out cake batter: Use a spatula or the back of a spoon to level out the cake mixture.
Bake: Bake in a preheated oven for between 20-25 minutes or until a skewer inserted in the middle comes out clean.
Remove from the oven and cool: After baking, remove from the oven and cool the cakes in the tin for 10 minutes, before turning onto a wire rack to cool completely.