Chocolate Walnut Mud Cake

from "the purple foodie" - http://purplefoodie.com/chocolate-walnut-mud-cake/ - recipe may be quartered and baked in a 4-inch springform pan

• Ready In: 1 hr
• Serves: 16
• Yields: 1 9-inch cake

Ingredients

• 8  ounces unsalted butter
• 1  cup all-purpose flour
• 2  teaspoons baking powder
• 1⁄2 teaspoon salt
• 12  ounces  semisweet chocolate
• 4  eggs
• 1  cup dark brown sugar, packed
• 1  teaspoon vanilla extract
• 1  cup  chopped walnuts, toasted
•  cocoa powder, to serve

Directions

1. Butter a 9-inch springform pan, then line the bottom with a disc of parchment paper. Use strips of parchment to line the sides as well.
2. Preheat an oven to 350°F (175°C).
3. Sift or whisk together the flour, baking powder and salt in a small bowl. Set aside.
4. In a saucepan over medium heat, melt the butter with the chocolate, stirring until smooth. Remove from the heat to cool slightly.
5. In a medium bowl, whisk together the eggs, sugar and vanilla so that the sugar is dissolved. The mixture should barely lighten in colour.
6. Pour the egg mixture into the chocolate, and stir to combine. Fold in the flour mixture, being careful not to overmix. Stir in the walnuts.
7. Pour the batter into the prepared pan and bake in a preheated oven for 35-40 minutes (15-17 minutes for 1/4th recipe) or until the centre is puffed and cracked. A cake tester inserted into one of these cracks should come out with wet, clumped crumbs; gooey but not liquid.
8. Let it cool in the pan for at least 15-20 minutes.
9. To serve, release the sides of the springform carefully and remove the parchment paper. If you’d like perfectly sharp slices, refrigerate it for a few hours before slicing.