For the cake
70 g (1/2 cup) walnuts, 250 g (about 3 medium) well-ripe bananas, 125 g (1 cup) all-purpose flour, ¾ teaspoon baking soda, ¼ teaspoon ground cinnamon, 1/8 teaspoon ground nutmeg and cardamom, a pinch of salt, 85 g (1/3 cup + 1 tablespoon) light brown sugar, 50 g (1/4 cup) granulated sugar, 2 large eggs, 1 teaspoon vanilla extract, 115 ml (1/2 cup) vegetable oil, 60 g (1/4 cup) sour cream
First, roast the walnuts in a 180 C (350 F) pre-heated oven until toasty-fragrant, about 12 minutes. Allow to cool then blitz to a meal in a high-powered food processor or blender, being cautious to stop short of damp clumps. Set aside until needed.
Grease and line a 20-cm (8-inch) square cake pan with non-stick parchment paper. Mash the bananas to a fleshy pulp.
In a large mixing bowl, sift together the flour, baking soda, cinnamon, nutmeg, cardamom and salt, then stir through the roasted walnut meal. In a separate bowl, add both sugars and eggs, followed by the vanilla, oil and sour cream, then whisk until combined. Mix in the banana pulp. Tip in the dry ingredients, then fold with a large rubber spatula, until just incorporated. Scrape into the prepared pan.
Bake for about 30 minutes, until golden brown and a skewer inserted into the middle comes out clean. Allow the cake to cool for 15 minutes, before lifting it out and onto a wire rack to cool completely before frosting.
For the frosting
250 g (1 cup + 2 tablespoons) cream cheese, 150 g (2/3 cup) unsalted butter, (soft), 60 g (1/2 cup) confectioners’ sugar, 55 g (1/4 cup) light brown sugar, 5 tablespoons hulled tahini (well-stirred), 1 teaspoon vanilla extract, a pinch of salt flakes, rose ras el hanout (page 229 of Wild Sweetness (2021 by Thalia Ho / published by Harper Design)
In the bowl of a stand mixer fitted with the paddle attachment, or, using handheld electric beaters, beat the cream cheese and butter until smooth and malleable. Pause mixing to scrape down the bottom and sides of the bowl, then add in the sugars, tahini, vanilla and salt flakes. Beat until an aerated buttercream has formed, a few minutes.
Frost the cake in swoops and swirls, then flourish the top with a pinch of rose ras el hanout. Decorate as desired. I like to chill the cake for about half an hour before slicing and serving it.
