1 pound	unsalted butter
1 pound	semisweet chocolate chips
6 ounces	unsweeted chocolate
6	eggs
1 tablespoon	instant espresso
2 tablespoons	vanilla extract
2¼ cups	granulated sugar
1¼ cups	all-purpose flour
1 tablespoon	baking powder
1 teaspoon	kosher salt
3 cups	chopped walnuts
12 ounces	semisweet chocolate chips

1. Heat oven to 350 degrees. Coat half-sheet pan with nonstick cooking spray.
2. Melt butter, 1 pound chocolate chips, and unsweeted chocolate in large bowl set over simmering water. Allow to cool slightly.
3. Mix eggs, espresso powder, vanilla, and sugar. Temper egg mixture into chocolate mixture. Allow to cool to room temperature.
4. Sift flour, baking powder, and salt. Fold into cooled chocolate mixture.
5. Stir in walnuts and 12 ounces chocolate chips. Pour into pan.
6. Bake for 30 to 35 minutes.