Preheat oven to 350 degrees F. Place a folded piece of parchment paper in a loaf pan and spray with nonstick spray. This will help remove the loaf later. Set aside.
In a large bowl, cream butter and sugar together for about 2 minutes until well combined. Add the egg then add the mashed bananas. Mix for 30 seconds, scraping down the sides of the bowl.
Add the flour, cocoa, baking soda, baking powder, salt and vanilla. Mix until well combined. Pour the mixture into the loaf pan. Bake for 45-65 minutes until a knife inserted in the center of the loaf comes out clean. Let cool for at least 30 minutes before cutting/serving.
To make the homemade whipped cream, whisk heavy whipping cream, sugar, and vanilla in a stand mixer, at high speed, for about 1 minute until you see soft peaks. Do not overmix or it will fall apart. Homemade whipped cream last 2-3 days in the fridge; 2-3 months in the freezer.
Serve chocolate banana bread slices with homemade whipped cream and raspberries (optional but delicious). Enjoy!