1/4 cup/70 grams all-purpose flour
1/4 tsp baking powder
1/8 tsp salt
1 1/3 cups/225 grams bittersweet chocolate, chopped (I use Ghirardelli 60% bittersweet chips)
2 tablespoons/28 grams unsalted butter
2 large eggs
1/2 cup/95 grams sugar
1 tsp vanilla extract
2 cups/200 grams walnuts or pecans, roughly chopped
1 cup/175 grams bittersweet chocolate, chopped into chunks (I use Ghirardelli 60% bittersweet chips)
Position the racks in the upper and lower thirds of the oven and preheat the oven to 350℉. Line two cookie sheets with parchment or wax paper.
In a small bowl, combine the flour, baking powder, and salt and stir with a small whisk to combine. Set aside.
Place the 1 1/3 cups of chocolate and the butter in a large heatproof bowl in a wide skillet of barely simmering water (you can also use a double boiler) and stir frequently just until melted and smooth. Remove the chocolate from the skillet and set it aside. Leave the heat on under the skillet.
In a large heatproof bowl, whisk the eggs, sugar and vanilla together thoroughly. Set the bowl in the skillet and stir until the mixture is lukewarm to the touch. Stir the eggs into the warm but not hot chocolate. Stir the flour mixture, then the nuts and chocolate chunks.
Scoop slightly rounded tablespoons of batter 1 1/2 inches apart on to the cookie sheets. Bake until the surface of the cookies looks dry and set but the center is still gooey, 12 to 14 minutes. If you used parchment paper, carefully slide the cookies, still on the parchment, onto racks or set the pans on the racks. Otherwise, let the cookies firm up on the pans for a minute, then transfer them to racks with a spatula. Let cool completely. Store in a tightly sealed container.