Whisk eggs and sugar just to combine, without whipping.
Mix in flour, baking powder, salt, lemon zest and vanilla, then gradually add melted butter until smooth.
Cover and chill for at least 6 hours, preferably overnight.
Pipe into a madeleine mould. Bake at 200°C, top/bottom heat, for 3 minutes. Without opening the oven, lower to 175°C and bake for 6–8 minutes until lightly golden. Unmould; cool completely.
Toast almonds at 155°C for 15 minutes. Dry 4 madeleines with the almonds and vanilla bean at 120°C for 15 minutes.
Cook sugar to an amber caramel; pour over almonds, madeleines and vanilla.
Cool completely, break up and blend with salt in a powerful blender until smooth and fluid.
Place white chocolate and butter in a blending jug.
Cook sugar to an amber caramel. Carefully stir in hot cream gradually and bring to a boil.
Pour over chocolate and butter. Add vanilla and salt, wait 1 minute, blend until smooth and cool.
Pipe caramel into each mould cavity, then praline. Add madeleines, ridged side toward the filling, domed side up. Press gently; freeze for 2 hours.
Unmould; clean and dry the mould thoroughly.
Pipe tempered chocolate into each cavity. Return madeleines, filled side toward the chocolate; press gently.
Chill for 10–15 minutes until set; unmould.
Refrigerate. Remove 10 minutes before serving.
