Preheat oven to 350 F. Spray a loaf pan with non stick spray.
In a small bowl, sift the flour, cocoa powder, baking powder and salt.
Beat butter and sugar until light and creamy.
Add eggs one at a time, beating well after each addition. Add vanilla extract and chestnut paste and beat well.
Using a rubber spatula, fold in the dry ingredients. Transfer to the prepared loaf pan.
Bake for 50-60 minutes, until a toothpick inserted comes out clean.
Cool for a few minutes before removing from pan.