Preheat the oven to 200C/180C Fan/Gas 6. Line three baking sheets with baking parchment.

In a heavy saucepan, melt the cubed butter in 250ml water over medium heat. Once melted, bring to a boil. Remove from heat; add sifted flour and stir until a soft ball forms. Return to low heat and cook for 3–5 minutes, stirring constantly. Let cool slightly.

Transfer the mixture to a mixer bowl and whisk in the beaten eggs gradually until smooth and shiny. Fill a piping bag fitted with a 1½cm plain nozzle with the choux mixture.

Pipe twelve small mounds of mixture onto each baking sheet (total 36). Smooth tops with a wet finger. Bake for 10 minutes at 200C, then reduce the oven to 190C/170C Fan/Gas 5 and bake for an additional 10 minutes until golden brown. Pierce each bun to release steam, then return to the oven for 5 minutes to dry out. Cool on a wire rack.

Heat milk in a heavy-based pan to boiling, then let cool for 30 seconds. Whisk egg yolks with caster sugar until pale, then add cornflour, cinnamon, and nutmeg. Gradually pour in warm milk, whisking continuously, then return to the pan. Cook over medium heat, whisking until thick and boiling for 1 minute. Remove from heat, cover, and cool.

Break milk chocolate into a heatproof bowl. Heat double cream until simmering, pour over chocolate, and stir until smooth. Cool until thick enough to drizzle.

Spoon melted white chocolate into a piping bag fitted with a writing nozzle. Pipe 12 snowflake shapes onto baking parchment and let set.

Whip double cream to soft peaks then fold into cooled crème pâtissière. Fill a piping bag with this mixture and pipe into cooled choux buns.

Boil caster sugar with 5 tablespoons water until golden (170C on a sugar thermometer). Remove from heat, plunge the pan briefly into cold water to thicken slightly.

On a cooling rack, arrange 14 choux buns in a circle. Place 10 buns inside to create a second circle. Dip one side of each bun in caramel and stick to the adjacent bun, forming a strong bond. Continue until both circles are joined.

Dip the bases of remaining 12 buns in caramel and place on top of the double circle wreath.

Line a baking sheet with silicone paper. Reheat caramel gently, add red food colouring paste, stir in hazelnuts, then place hazelnuts individually on silicone paper to cool and harden.

Drizzle one quarter of the chocolate ganache over the wreath. Transfer to a serving plate and decorate with white chocolate snowflakes and caramel-coated hazelnuts. Serve immediately.