Line a brownie pan or 8 or 9 inch cake pan with parchment. Preheat the oven to 350 deg F (180 C).
Mix all the wet ingredients in a bowl until well combined.
Add the dry ingredients and mix until just about combined. The batter will be thick. Spread evenly in the prepared pan.
Bake for 30 mins. 5 mins less or more depending on the pan used. Taller cake will need longer time. Check with a toothpick inserted in the middle. It should come out clean. For muffins or cupcakes, bake for 20 to 22 mins.
Cool for 5 mins, then remove from the pan and cool completely before frosting. At this point you can optionally brush the cake with a mix of 1 tbsp maple syrup+ 2 tsp water(mix well in a small bowl). This keeps the cake more soft and moist.
Make the ganache: Heat pumpkin puree and milk over medium heat until bubbling hot. Add chocolate, whisk for a few seconds, then take off heat. Continue to whisk until all the chocolate is melted and the mixture is smooth.
Cool for 5 mins then chill for 15 mins to thicken. Then then spread over the cake. Add other garnishes such as chopped hazelnuts, coconut or candied pecans. Serve. The frosted cake can be refrigerated for upto 4 days. Frozen for upto a month
Gluten-free: Make this GF Sweet Potato Cake with pumpkin puree and add this chocolate ganache instead of the crumb.Nutrition is for 1 slice