6 ounces semi or bittersweet chocolate chips
1/2 cup flour
1/4 cup cocoa powder
1 teaspoon instant espresso granules
1/2 teaspoon sea salt
8 tablespoons butter, cut into pieces
1 teaspoon vanilla extract
2 large eggs
3/4 cup sugar
1 cup walnuts, chopped (optional)
Preheat oven to 350ºF. Grease an 8-inch square glass baking pan; set aside. Measure out 1/4 cup of the chocolate chips and set aside. In a small bowl, whisk together the flour, cocoa, espresso powder and salt; set aside.
Add remaining chocolate chips to a medium bowl with the butter. Cook on high power in the microwave for 60 to 90 seconds until chocolate and butter are melted. (You can also mel the chocalate chips and butter under doibler water). Add the vanilla extract to the bowl and stir to combine; set aside.
Add the eggs and sugar into a clean, large bowl. Whisk until thick and pale yellow. Whisk in the melted chocolate mixture. Using a rubber spatula, fold in the flour mixture and remaining chocolate chips. Pour batter into prepared pan. Evenly sprinkle chopped nuts over top, if using, and press very gently into the batter. Bake for 40 minutes until center is set and edges gently pull away from the sides of the pan. Let cool completely before cutting.