Preheat the oven to 350 degrees F.

Grease and line two 9" cake pans with parchment paper.

Soak two cake strips in ice water.

In a medium bowl, combine the flour, baking powder, baking soda, and cinnamon.

In a large bowl, vigorously whisk together the sugars, eggs, vanilla, and salt.

Add the oil and milk, and mix until fully combined.

Add the dry ingredients, whisking until just barely combined.

On a large plate, mash the over-ripe bananas with a fork until smooth. Then, whisk the mashed banana into the batter.

Divide the batter between the cake pans. Wrap the cake strips around the outside of the pans, then bake the cakes for about 32-38 minutes or until golden on top and the sides of the cake start to pull away from the edges.

Allow the cake layers to cool in the pan for a few minutes then turn out onto a wire rack to cool completely.

Once cool, wrap each cake in plastic wrap and place in the freezer until ready to decorate. (Frozen cake layers are much easier to frost!)

Place the egg yolks and 24g (2 tbsp) of granulated sugar in a medium bowl or a bowl of a stand mixer fitted with a whisk attachment. Whisk on high speed until thick and foamy (about 3 minutes) while you heat the sugar and water.

Heat the remaining 100g (½ cup) of granulated sugar and water in a small saucepan over low heat, stirring constantly until the sugar dissolves. Increase the heat to medium and bring to a boil, or until it reaches 240 degrees F.

While the egg yolks are whisking on medium speed, slowly add the sugar syrup into the bowl. Continue mixing until the mixture has cooled down.

Add the butter to the mixture a few cubes at a time, allowing them to fully incorporate before adding more.

Lastly, add the nutella. Continue mixing on low speed until the frosting is completely smooth.

Transfer ¼ of the frosting to a piping bag.

In a medium bowl, combine the nutella and hazelnuts.

Place the first cake layer on a cake stand. Pipe a dam of frosting around the edge of the cake. Fill the center with the nutella hazelnut filling.

Add the second cake layer and top with a few scoops of frosting. Use an offset spatula to smooth out the top, and spread the excess all over the sides.

Continue decorating the cake as desired. Pipe dollops of nutella along the edge of the cake and top with hazelnuts. Use a sharp knife to cut individual slices, and enjoy!