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Ingredients
Lemon Sponge Base (1 x 8-inch layer)
- 85 g plain flour
- 2 g baking powder ½ tsp
- 1 g bicarbonate of soda ¼ tsp
- Pinch salt
- 67 g unsalted butter softened
- 80 g caster sugar
- 1 medium egg room temperature
- 60 g sour cream
- 4 ml vanilla extract 1 tsp
- 12 ml fresh lemon juice
- Zest of 1 lemon approx. 2 tsp
- 50 ml whole milk
Tangy Lemon Curd
- 6 egg yolks
- 1 whole egg lightly beaten
- 160 g caster sugar
- 95 ml fresh lemon juice
- Zest of 2 lemons approx. 2 tbsp
- Pinch of salt
- 56 g unsalted butter cubed
Tangy Lemon Curd
- 9 g powdered gelatine
- 36 ml cold water
- 270 g good-quality white chocolate finely chopped
- 570 ml double cream cold (divided: 190ml + 380ml)
- 65 g prepared lemon curd from above
Method
Lemon Sponge
- Preheat your oven to 180°C (160°C Fan / Gas 4). Grease an 8-inch round cake tin and line the base with baking parchment.
- In a small bowl, whisk together the plain flour, baking powder, bicarbonate of soda, and salt.
- In a separate mixing bowl, beat the softened butter and caster sugar for 3–4 minutes until pale and creamy.
- Beat in the egg until fully incorporated, followed by the sour cream, vanilla extract, lemon juice, and lemon zest.
- Fold in the dry ingredients alternating with the milk until you have a smooth, lump-free batter.
- Transfer to the prepared tin, level the surface, and bake for 18–22 minutes until golden and a skewer inserted in the center comes out clean.
- Allow to cool completely on a wire rack.
Lemon Curd
- In a medium saucepan, whisk together the egg yolks, whole egg, caster sugar, lemon juice, lemon zest, and pinch of salt.
- Place over medium-low heat and cook, stirring constantly with a whisk or silicone spatula, for 8–10 minutes until thick enough to coat the back of a spoon.
- Take off the heat and pass through a fine-mesh sieve into a clean bowl to ensure a silky-smooth finish.
- Stir in the cubed butter until melted and glossy.
- Press a sheet of cling film directly against the surface of the curd and chill in the fridge until completely cold.
White Chocolate Mousse
- Sprinkle the powdered gelatine over the 36ml of cold water in a small ramekin and leave to bloom for 5–10 minutes.
- Place the chopped white chocolate into a heatproof bowl.
- Heat 190ml of double cream in a small saucepan over medium heat until steaming and just beginning to simmer around the edges (do not let it boil).
- Remove the cream from the heat, add the bloomed gelatine, and stir until completely dissolved.
- Pour the hot cream-gelatine mixture directly over the white chocolate. Let it sit undisturbed for 1 minute, then whisk gently until smooth and fully melted. Let cool to lukewarm/room temperature.
- In a separate large bowl, whip the remaining 380ml of cold double cream to medium-soft peaks.
- Gently whisk 65g of the cooled lemon curd into the cooled white chocolate mixture.
- Fold the whipped double cream into the chocolate mixture in 2–3 additions using a spatula until uniform, light, and airy.
Assembly & Finish
- Place the cooled sponge layer into the base of an 8-inch springform tin or cake ring lined with an acetate collar for neat, clean edges.
- Pour the white chocolate mousse over the sponge layer, smoothing the top with an offset spatula.
- Place into the fridge to chill for at least 2 hours until the mousse is set and firm to the touch.
- Gently warm the remaining lemon curd if it has become too stiff, then spread an even layer across the top of the firm mousse.
- Return the cake to the fridge to set completely for at least 4 more hours (or overnight).
- Remove the springform ring, carefully peel away the acetate collar, and garnish with fresh lemon twists, white chocolate shavings, or fresh berries before slicing.