Grease the interior of a 7 inch springform baking pan. Line the bottom and inner sides with parchment paper.
In a large microwave-safe bowl, add chocolate chips. Microwave at 1 minute intervals, stirring in between with a spatula, until chocolate is fully melted and smooth. (I needed 2 minutes total cooking time). Alternatively, you can melt the chocolate on the stove using the double boiler method.
Stir in the pumpkin puree until fully combined. Use your spatula to scrape chocolate from the sides and bottom of the bowl to make sure it is fully incorporated with the pumpkin. You don't want any batter that is just chocolate or just pumpkin.
Pour batter into prepared pan. Use your spatula to smooth the surface. If you have an icing smoother, you can use that on the surface of the cake to make it even more smooth. Bang the bottom of the pan a few times against your counter to level the cake and remove any air bubbles.
Place into fridge until cake is set. This can take 30-60 minutes. Once cake is set, you can decorate if desired. Slice cake with a sharp knife. Store uneaten cake in the fridge.
Notes
To make the optional chocolate ganache frosting you will need 2 oz heavy cream and 1/2 cup (91 g) semi-sweet or bittersweet chocolate chips. Place chocolate chips in a mixing bowl. Heat heavy cream until it reaches a simmer. Pour the heavy cream over chocolate. Immediately start stirring until chocolate is completely melted and smooth. Pour ganache over cake and spread it out across the surface. Place the cake in the fridge until ganache is set. This recipe will give you a thin layer of ganache frosting. If you want a thicker layer, double the recipe. The cake in the photos has a double layer but the cake is so rich that I found a thin single layer was enough.
If using banana puree, make sure to actually puree it in a food processor or blender. See post for more details about the difference between using pumpkin vs banana.
Make sure to use fresh bananas. Frozen bananas retain too much water.
This recipe does not work well with applesauce as a substitute.
This cake is best made in a springform pan as it will be easier to remove. I made mine in this 7 inch pan.* You can make it in a smaller pan, your cake will just be thicker. I don't recommend making it in anything bigger than 7 inches because your cake will be quite thin.
The estimated nutrition is for the cake only, not including frosting.
*This product link is an affiliate link. This means I earn a small commission from qualifying purchases.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.