Preheat the oven to 180*C.

Whisk together butter and sugar until fluffy and light in colour.

Add eggs, one at a time, whisking after each addition until well combined.

Add vanilla essence and mix.

Now add flour and baking powder.

Whisk until well combined.

Melt chocolate.

Divide the batter into 2 parts.

Mix chocolate in one part.

Line a loaf pan with baking paper. Add half of the plain batter, then add chocolate batter and top with vanilla batter.

Bake in a preheated oven for 10-25 minutes or until the toothpick inserted comes out clean.

Take out and allow to cool to room temperature in the same pan.

Slice the cake and serve with tea or coffee.