Step 1

Preheat oven to 325 degrees F (165 degrees C). Grease a deep baking pan.

Step 2

Melt chocolate and butter in top of a double boiler over simmering water, stirring frequently and scraping down the sides with a rubber spatula to avoid scorching.

Step 3

Mix eggs and vanilla extract together in a large bowl; mash bananas into egg mixture until well mixed.

Step 4

Combine flour, sugar, cocoa powder, and baking powder in a separate bowl.

Step 5

Mix chocolate mixture into the banana mixture; add flour mixture and stir until smooth. Pour mixture into the greased baking pan.

Step 6

Bake in preheated oven until top is dry and edges have started to pull away from the sides of the pan, about 60 minutes.