Preheat your oven to 350°F (175°C).
Grease a 9x13 inch baking pan.
Melt the butter in a saucepan over low heat.
Remove from heat and stir in the sugar, eggs, and vanilla.
In a separate bowl, sift together the flour, cocoa, and salt.
Add the dry ingredients to the wet mixture and stir until just combined.
Fold in chocolate chips if using.
Pour the batter into the prepared baking pan.
Bake for 25-30 minutes, until a toothpick comes out with a few moist crumbs.
Let cool before cutting into squares and dusting with powdered sugar.