For the Brownies:
Preheat oven to 350F. Butter the bottom and sides of a 9 by 13 inch metal baking pan. Put a long piece of parchment paper in the bottom of the pan, letting the parchment extend up two sides of the pan and overhang slightly on both ends. Butter the parchment.
In a medium saucepan over medium heat, melt the butter. Remove from heat and add the sugar; stir to combine. Beat in eggs and vanilla until combined.
Mix in cocoa, baking powder and salt. Add flour and stir until just combined. Pour into prepared pan and spread into an even layer. Bake for bake 25-30 minutes. Let cool completely in pan on a cooling rack.
For the Frosting:
While the brownies are cooling, make the frosting. Beat butter, hot fudge sauce, honey, and vanilla until blended. Add powdered sugar and beat to desired consistency.
Pour over brownies.
Chill to set the frosting until ready to serve (if desired).