Preheat oven to 150 C / 300 F. Butter a loaf pan.

In a large bowl sift together flour, cocoa powder, baking powder, and salt. Set aside.

Place oil and sugar in a stand mixer bowl. Beat on medium high until mixture is blended.  
Add the eggs, yogurt, milk and the flour mixture.

Beat mixture until it becomes light and fluffy.

Stir in 1 cup chocolate chunks. Pour mixture into loaf pan

Bake for about 1 hour. Let the cake cool for 10 minutes on a wire rack, then turn it out from the pan and let it cool completely.

Melt the remaining chocolate chunks separately in pan over barely simmering water, then use a spoon to drizzle over the cake. Leave to set before slicing.