Step 1

Preheat oven to 190°C. Grease a 20cm springform pan with oil or butter. Line the bottom and side of the pan with baking paper and set aside.

Step 2

Place egg yolks and muscovado sugar in the bowl of a stand mixer fitted with the whisk attachment (or in a large bowl, if using a hand-held electric mixer). Whisk on high for about 2 minutes, or until pale and fluffy, scraping down sides of the bowl as necessary. Transfer mixture to a large bowl. Add walnut, lemon zest and 1/4 tsp salt flakes and mix well to combine.

Step 3

Clean and dry the stand mixer bowl and whisk attachment, then add egg whites to the bowl. Whisk on high for 2 minutes, or until stiff peaks form. Using a spatula, fold egg whites into the walnut mixture a third at a time; the mixture will be thick and quite difficult to bring together at first but will gradually loosen, so the final addition of whites lightens the batter considerably.

Step 4

Pour batter into prepared pan and bake for 40 minutes, until evenly puffed. This is a moist cake, so a skewer inserted inside should not come out completely clean.

Step 5

Let cake cool for 5 minutes, then release it from the pan. (You may need to run a small knife around the edge.) Carefully flip over cake, remove pan and paper from the bottom, and flip again to transfer to a large plate. Brush surface with amaretto and leave to cool completely.

Step 6

While cake is cooling, make the caramelised walnuts. Sprinkle sugar evenly over the base of a medium saucepan and place over medium heat. Cook gently for about 6 minutes, swirling pan but resisting the urge to stir, until you get a medium brown syrup, the consistency of maple syrup. Add walnuts and quickly stir into the syrup until coated. Pour nuts onto a parchment-lined baking tray, spread in a single layer, and sprinkle with a pinch of salt flakes. Once cool and hardened, roughly chop into 1cm and 2cm pieces.

Step 7

To serve, add cream and sugar to the bowl of a stand mixer fitted with the whisk attachment (or use a large bowl and a hand-held whisk). Whisk on high speed for 1 minute, or until firm and fluffy. Once the cake has cooled, spread cream over surface and scatter with caramelised walnuts to serve