Melt 7 oz (200 gr) bittersweet chocolate in a double boiler or microwave. Remove from heat and allow to cool slightly.
Preheat oven to 350F/180°C. Grease the mini loaf pans and line them with a strip of parchment paper each.
In a large bowl, whisk eggs, sugar, yogurt, oil, melted chocolate, and vanilla until well incorporated.
Stir in flour, baking powder, baking soda, and salt with a spatula until well combined. Stir in the chocolate chunks (optional).
Gently pour the batter into the prepared loaf pans. Bake for 25 minutes, until a toothpick inserted comes out clean. Remove from oven, allow to cool slightly before removing from the loaf pans, then cool completely on a wire rack.
After the loaf cakes have cooled down, garnish with melted chocolate and pistachios (optional).