Preheat the oven to 350 F. Grease a 9x9 inch square cake pan. Sprinkle some flour around the pan and shake it around until the inside of the pan is covered. Tap out the excess flour. Set aside.

In a stand mixer with a whisk attachment, combine the eggs, egg yolks, powdered sugar, and hazelnut flour. Whip the mixture on high speed until doubled in volume, about 3-5 minutes. Transfer the mixture to a large bowl.

Clean the mixer bowl and whisk. Place the egg whites into the mixer bowl and whip on medium high speed until bubbles start to form, about 2 minutes. On low speed, gradually add the granulated sugar and mix until the mixture is shiny and holds medium stiff peaks, about 5-7 minutes.

Using a rubber spatula, scoop a quarter of the egg white mixture into the egg yolk mixture. Gently fold them together until they’re fully combined. Add the rest of the egg white mixture and gently fold until just combined. It’s okay to have some streaks of the egg white mixture visible. Gently fold in the all-purpose flour until it’s fully incorporated.

Transfer the batter to the prepared cake pan. Bake for 25 minutes, or until the cake is lightly golden brown.

Let the cake cool in the pan for 15 minutes before transferring it to a wire rack to cool completely.

In a medium bowl, beat the butter until smooth.

On low speed, add the Nutella, powdered sugar, vanilla extract, and milk and beat until combined.

Beat the frosting on medium-high speed until fluffy. Set aside until ready to assemble the cakes. If needed, you can place the frosting in the refrigerator.

Using a serrated knife, cut the edges of the cake off so that it’s level.

Next, cut the cake vertically down the center so you have two small rectangles. If needed, level the tops of the cakes using the serrated knife.

Place a few spoonfuls of frosting on the top of one of the rectangles. Use an offset spatula to spread the frosting into an even layer.

Place the second rectangle on top of the frosting so that the bottom of the cake is on top.

Use the serrated knife to make two horizontal cuts across the cake, dividing the cake into three separate smaller rectangles.

Cut the corners off of the rectangle cakes to mirror Thor’s Hammer’s edges.

Place a couple spoonfuls of frosting onto one of the cakes. Use an offset spatula to frost the cake, making the frosting evenly covers the top and sides. Repeat with the remaining two cakes. Place the cakes in the refrigerator to set, about 20 minutes.

Meanwhile, divide the silver fondant into three chunks. Work with one chunk at a time, storing the rest in the container so it doesn’t dry out.

Place the fondant on a piece of wax or parchment paper and roll out to about ¼ inch thickness.

Drape the fondant over one of the cakes. Gently press and pull the fondant over the cake until it is smooth. Cut off any excess fondant as you go. Repeat with the remaining two cakes.

Use a small knife to cut a hole in the centers of the cake. Gently press one of the pirouette cookie halves into the hole to make the hammer’s handle. Repeat with the remaining two cakes.