Preheat oven to 350 degrees. Butter a 13 by 9-inch baking dish and line with one long sheet of parchment paper or aluminum foil, leaving an overhang on two sides. Butter parchment paper (or foil), set aside.
In a mixing bowl, stir together melted butter and cocoa powder until well blended. Mix in sugar and salt. Using a wooden spoon, blend in eggs one at a time. Stir in vanilla extract then add flour and stir until no streaks of flour remain.
Pour into prepared baking dish. Bake in preheated oven 18 - 20 minutes, until toothpick inserted into center comes out with a few moist crumbs attached. Set baking dish on a wire rack and cool completely.
Using overhang of parchment, lift brownies from pan. Using a 2 1/2-inch round cookie cutter or biscuit cutter, cut brownies into rounds*.
Frost each round with cream cheese frosting (pipe or spread) then top with fresh fruit (for the bananas I tossed in a light lemon water mixture then dried so they didn't brown so quickly).
For best results serve just after assembling (you can make both the brownies and frosting ahead of time, you can even frost them the day before and refrigerate them, just add the fruit just before serving).
For the Cream Cheese Frosting:
In the bowl of an electric stand mixer fitted with the paddle attachment, whip cream cheese and butter until smooth and fluffy. Mix in vanilla then add powdered sugar and continue to whip mixture until smooth and fluffy.
*For an easier method, bake brownies in a whoopie pie pan or bake in the 13 by 9 and skip the cutting into rounds part, simply frost the entire layer, top with fruit then cut into bars.
*I got 14 rounds. The tops crack a little but that's fine because they are frosted anyway. Also they'll stick to the cookie cutter since the brownies are so moist, so just carefully push down on the edges of brownie being cut when lifting cookie cutter up)