Step 1

Preheat oven to 180 C (350 F).

Step 2

Line 20x20 cm (8x8 inch) baking pan with parchment paper.

Step 3

In a bowl whisk flour, cocoa powder, and salt.

Step 4

Melt butter, Nutella, chocolate and coffee (if using) in a double boiler or water bath. Leave it to cool while you mix eggs.

Step 5

With an electric mixer beat eggs and sugar, until frothy, about 3-4 minutes, beat in vanilla.

Step 6

Pour egg mixture in melted chocolate and whisk until blended.

Step 7

Using a rubber spatula fold in dry ingredients.

Step 8

Pour the batter into prepared baking pan and bake for 20-25 minutes.