Pre-heat oven to 350?F. Grease an 8x8 square pan or a 9x5 loaf pan or line with parchment or foil; set aside.

In a large microwave-safe mixing bowl, add the butter and microwave for 1 minute or until completely melted. Add the sugar and cocoa powder and whisk vigorously for at least a minute, until the sugar has dissolved.

Add eggs one at a time then vanilla and whisk for at least 1 minute, until well combined and batter is shiny.

Stir in flour and salt until the flour is fully combined. Be careful not to overmix.

Optional: Fold in 1/2 cup of nuts, raisins, chocolate chips or anything you desire.

Spread in pan and bake for approximately 20 minutes or until the center is slightly set. Be careful not to over-bake!

Cool completely then cut into 9 large squares or 16 small squares.