Method

• 1.
  For the marinated rhubarb, put the rhubarb in a heatproof bowl with sugar and citric acid. Toss it together and cover with biodegradable plastic wrap. Make a bain-marie by placing the bowl over a saucepan of simmering water (don’t let base of bowl touch the water) and leave for about 20 minutes, or until the fruit is soft. Gently remove the rhubarb, strain and reserve the syrup (this makes a great cordial for a cocktail or soda water – thank me later). Set aside.
• 2.
  Meanwhile, for the cake, preheat oven to 185°C/165°C fan-forced. Melt the butter in a small saucepan over medium heat until it starts to foam. Reduce the heat to low and continue to cook, stirring occasionally, until it stops fizzing and turns mid-brown. Cool slightly.
• 3.
  In a medium bowl, stir together the almond meal, plain flour, baking powder and ½ tsp fine salt. Using a stand mixer fitted with the whisk attachment on low speed or whisking by hand, slowly combine the egg and sugar until the sugar has dissolved – you don’t want to incorporate any air at this stage. With the mixer still running or while hand-whisking constantly, slowly add the brown butter. Ensure that the mixture is well combined, so that the butter doesn’t bleed out later and give the cake a greasy texture. Mix in the dry ingredients, making sure there are no lumps. Pour the batter into a deep 20cm (2.75L) baking dish, scatter the marinated rhubarb evenly over the top and bake for about 25 minutes, or until the crust is golden brown and the centre is firm.
• 4.
  Meanwhile, for the white chocolate custard, bring the milk, lemon myrtle and ¼ tsp (2g) fine salt to a simmer in a large saucepan over medium heat. Whisk the egg yolk and cornflour together in a large heatproof bowl. Strain the hot milk through a sieve directly into egg mixture, whisking quickly to combine until there are no lumps. Pour back into the pan, return to the heat and, whisking constantly, bring to a simmer. Remove from the heat, then add the chocolate and whisk until combined. Using a stick blender, blend until the mixture is shiny and smooth, keeping the head of the blender fully submerged to ensure no air is incorporated into the mix (you can also transfer mixture to a blender and blend until smooth). Decant into a jug to use straight away – you want to keep it as warm as possible so that it cooks nice and evenly in the next step.
• 5.
  When the cake is cooked, leave in the oven and carefully pour the hot custard on top of the cake layer. Reduce oven temperature to 145°C/125°C fan-forced and bake for 30 minutes, or until the custard has a very slight wobble in the centre. Cool completely in the baking dish.
• 6.
  Once cooled, dust the top with a little caster sugar and brulee with a kitchen blowtorch until deep golden brown.