This cake is swirled and topped with chocolate ganache. If you aren’t topping the cake with ganache, halve the ganache recipe so you’re only making what you need for the swirl. (Use one 4 ounce chocolate bar and 1/2 cup (120ml) heavy cream.)

Place chopped chocolate in a medium heat-proof bowl. Heat the cream in a small saucepan over medium heat until it begins to gently simmer. (Do not let it come to a rapid boil– that’s too hot!) Pour over chocolate, then let it sit for 2-3 minutes to gently soften the chocolate. Very slowly stir until completely combined and chocolate has melted. The finer you chopped the chocolate, the quicker it will melt with the cream. You should have about 1 and 1/2 cups of ganache. Set half aside (3/4 cup or 180ml) at room temperature uncovered until it has thickened into a gravy-like consistency, about 30 minutes. Use this in step 7. Cover and refrigerate the rest of the ganache to use as the topping in step 10. Ganache topping can be refrigerated for up to 5 days before using.

Preheat the oven to 350°F (177°C) and generously grease a 10-inch Bundt pan. To guarantee the Bundt cake releases seamlessly, I strongly recommend using a heavy coating of nonstick spray. Our favorite pans include this one and this one.

Mash the bananas until there’s hardly any lumps. I usually just use my mixer for this! Set mashed bananas aside.

Whisk the flour, baking powder, baking soda, cinnamon, and salt together. Set aside.

Using a handheld or stand mixer fitted with a paddle attachment, beat the butter on high speed until smooth and creamy, about 1 minute. Add both sugars and beat on high speed for 2 minutes until creamed together. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) Scrape down the sides and up the bottom of the bowl with a silicone spatula as needed. Add the eggs and the vanilla. Beat on medium-high speed until combined, then beat in the mashed bananas. Mixture will be chunky and appear curdled—that’s ok. Scrape down the sides and up the bottom of the bowl as needed. With the mixer on low speed, add the dry ingredients in three additions alternating with the buttermilk and mixing each addition just until incorporated. Do not over-mix. The batter will be thick with some lumps. Makes about 6 cups of batter.

You will use the slightly thickened ganache reserved for the swirl in this step. Pour about 1/3 of the cake batter (about 2 cups) evenly into prepared pan. Drizzle half of the ganache on top (about 6 Tablespoons). Swirl with a knife or toothpick. Evenly pour another 1/3 of the cake batter on top, followed by the rest of the ganache (about 6 Tablespoons), then the rest of the cake batter. Swirl everything together with a knife or toothpick. See photo above for a visual.

Bake for 60-75 minutes or until a toothpick inserted into the cake comes out clean with just a couple lightly moist crumbs. This is a large, heavy cake so don’t be alarmed if it takes a little longer in your oven. If the cake is browning quickly in the oven, tent it with aluminum foil to help it bake more evenly.

Once done, remove from the oven and allow to cool for 2 hours inside the pan. Then, invert the slightly cooled cake onto a wire rack or serving dish. Cool completely before topping, slicing, and serving.

The ganache topping will be very thick by now. Warm it over low heat on the stove stirring constantly until thinned and drizzle-able consistency. Do not over-heat it. Or warm in 10 second increments in the microwave, stirring after each until thinned. Drizzle over cake, then slice and serve.

Cover leftover cake tightly and store at room temperature for up to 2 days or in the refrigerator for up to 5 days. Cake tastes unbelievable warmed in the microwave for a few seconds and served with vanilla ice cream.