Pre-heat oven to 350F. 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 mix.
    (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 

Notes
For EXTRA gooey brownies: Add 1 tablespoon oil of choice to the batter along with the butter.
For espresso flavor: add 1 teaspoon of instant coffee or espresso powder to boost the chocolate flavor.
Doubling the recipe: This recipe also doubles well in a 9x13 pan or 9x9 pan, add 5-7 minutes of baking time. To double, adjust the serving size above to 32. 
The sweetness: The recipe calls for 1 cup of sugar; feel free to use between 3/4 cup - 1 1/4 cup depending on your personal preference! 
Don't over-bake. Be sure to bake these brownies for no more than 20-25 minutes. Overbaking the brownies will make them dry and cakey.