-
Preheat oven to 350 degrees. Line a 9 x 13 inch pan with tinfoil. Lightly grease tinfoil with cooking spray.
-
Put butter and chocolate broken into pieces into a large microwave safe bowl. Microwave on high for 30 second intervals stirring in between until melted and smooth. Set aside.
-
In your mixer beat eggs, sugar and vanilla until light and fluffy, 3-5 minutes, scrapping sides and bottom of bowl half way through. Turn mixer on low and slowly add melted chocolate; beat until combined.
-
Add the flour and salt. Mix until just combined. Mix in chocolate chips and walnuts, if desired.
-
Pour batter into your prepared pan.
-
Bake for 45-50 minutes or until a toothpick inserted comes out slightly moist. Remove from oven and let sit until cooled.