First, preheat the oven to 180c Fan / 200c Electric / Gas mark 4. Then lightly grease a brownie tin (about 9x13in sized tin) and line with baking paper.

Next, sieve the flour, caster sugar and baking powder into a large mixing bowl, then stir in the brown sugar and salt.

Make a small well in the centre of the dry ingredients and add about half of the milk and whisk together using an electric whisk, on a low speed.

While still whisking, add the oil and ensure everything is mixed together, then pour in the rest of the milk and whisk until the mixture is smooth.

Break up the chocolate into small pieces, this can be done by placing it in to a food bag and giving it a good few whacks with a wooden spoon or rolling pin. Fold the chocolate pieces into the mixture, making sure they are spread evenly and then mix in the vanilla essence.

Pour the mixture into the brownie tin and place the walnut pieces on the top. This can be done any way you like. I like to have a walnut piece for each brownie, so I spread about 20 walnut pieces out evenly.

Pop the brownies in the centre of the oven for around 25-30 minutes.

When ready, remove from the oven and leave them to cool in the brownie tin, for about 10 minutes before serving.