Equipment
Ingredients
Walnut Sponge
- 150 g walnuts, toasted
- 200 g all-purpose flour
- 8 g baking powder
- 3 g kosher salt
- 200 g unsalted butter, room temperature
- 200 g granulated sugar
- 4 eggs, room temperature
- 60 ml whole milk, room temperature
- 10 ml vanilla extract
Caramelised Walnuts
- 100 g granulated sugar
- 30 ml water
- 15 g unsalted butter
- 2 g kosher salt
- 150 g walnut halves, toasted
Vanilla Buttercream
- 300 g unsalted butter, room temperature
- 300 g powdered sugar, sifted
- 30 ml heavy cream, room temperature
- 10 g vanilla bean paste
- 2 g kosher salt
Nutrition (per serving)
Method
Preheat the oven to 175 C or 350 F. Grease two 20cm round cake pans and line the bottoms with parchment paper.
Place the 150g of walnuts for the sponge into a food processor and pulse until finely ground, resembling coarse almond meal. Do not over-process into a paste.
Sift the all-purpose flour, baking powder, and salt into a medium bowl, then whisk in the ground walnuts until evenly distributed.
In a stand mixer fitted with a paddle attachment, beat the softened butter and granulated sugar on medium-high speed until incredibly pale and fluffy.
Add the room temperature eggs one at a time to the butter mixture, beating well after each addition and scraping down the bowl, then mix in the vanilla extract.
Gently fold the dry walnut and flour mixture into the wet ingredients in three additions, alternating with the whole milk, beginning and ending with the dry ingredients.
Divide the batter evenly between the prepared cake pans and bake at 175 C or 350 F until a wooden skewer inserted into the center comes out clean. Once baked, let cool in pans for 10 minutes before turning out onto a wire rack to cool completely.
For the caramelised topping, combine granulated sugar and water in a medium saucepan over medium heat. Cook without stirring, only gently swirling the pan, until it reaches a deep amber color.
Remove the caramel from heat immediately, add the butter, salt, and walnut halves, stirring quickly to coat. Spread them onto a parchment-lined baking sheet to cool.
Prepare the buttercream by whipping the softened butter in a clean stand mixer bowl on high speed until extremely pale and creamy.
Gradually add the sifted powdered sugar to the whipped butter on low speed. Once incorporated, pour in the heavy cream, vanilla bean paste, and salt, then increase speed to high and beat until light and airy.
Level the cooled cake layers with a serrated knife if necessary. Place one layer on a serving plate, spread an even layer of buttercream, and top with the second cake layer. Frost the top and sides smoothly with the remaining buttercream.
Break the cooled caramelised walnuts into clusters and arrange them decoratively over the top of the frosted cake.
Chef's Notes
- Toasting the walnuts lightly before grinding them for the sponge will dramatically elevate the depth of flavor in the final cake.
- For the silkiest American buttercream, beating the butter alone for at least five minutes before introducing any powdered sugar is crucial. It incorporates air and whitens the butter.
- When making the caramel, adding a tiny drop of lemon juice to the sugar and water can help prevent premature crystallization.
- If your environment is exceptionally warm, you may need to chill the cake for 15 minutes after the first crumb coat of frosting before applying the final layer of buttercream.
Storage
Refrigerator: 5 days — Store in an airtight container or cake dome. Bring to room temperature for 1 hour before serving to soften the buttercream.
Freezer: 2 months — Freeze slices individually wrapped tightly in plastic wrap and aluminum foil.
