Combine milk chocolate and dark chocolate in medium-sized bowl

Stir sugar, 2 tbs water, and cinnamon stick in heavy medium saucepan over medium-low heat until sugar dissolves. Increase heat and boil without stirring until syrup turns deep amber, occasionally brushing down sides of pan with wet pastry brush and swirling pan, about 6 minutes (time will vary depending on size of pan). Add cream and salt (mixture will bubble vigorously). Bring caramel to boil, whisking until smooth and caramel bits dissolve, about 1 minute. Discard cinnamon stick

Pour the hot caramel over chocolate; stir until chocolate has melted and mixture is smooth

Let stand until completely cool, stirring occasionally, about 1 hour

Using an electric mixer, beat butter in large bowl until fluffy

Beat in the chocolate mixture in 4 additions

Cover and refrigerate the ganache overnight

Preheat oven to 175ºC/350°F/gas mark 4

In a medium-sized mixing bowl, sift together the flour, cornflower, baking powder and salt

In another bowl and using an electric mixer, beat the butter until pale & fluffy

Add 200g/7oz of the sugar, egg yolks and vanilla extract and combine well

Add the chestnut spread, then the milk and combine well

Sift the dry ingredients over and carefully mix together

In another large bowl, and using clean beaters, beat the egg whites into soft peaks

Add the remaining 50g/1¾oz sugar and beat until stiff but not dry

Fold the egg whites into the batter in 3 additions

Transfer batter equally across the prepared cake tin(s) (kitchen scales can be useful for this - I made it about 325g per tin)

Bake the cakes until golden and a skewer inserted into the middle comes away clean (about 25-30 minutes)

Allow to cool completely in the pan(s) on a wire rack

Stir the rum and brown sugar in small bowl until the sugar completely dissolves

Turn cakes out onto work surface and peel off the parchment

Place one of the cakes, bottom side up, on a clean piece of parchment

Brush the cake layer with ¼ of the rum syrup

Spread with ¼ of the ganache and sprinkle with ¼ of the chopped chestnuts

Top with second cake layer, bottom side up

Repeat this twice - ¼ rum syrup, ¼ ganache, and ¼ chopped chestnuts

Top with the fourth, final cake layer, bottom side up

Spread the remaining ¼ of the ganache over the top and sides of the cake

Place cake rack on sheet of foil; place assembled cake on rack

Chill while you prepare glaze

Bring cream, sugar, and 60ml/2fl oz water to boil in heavy medium saucepan, stirring until sugar dissolves

Add the chocolate and whisk until melted and the glaze is smooth. Allow to cool until thick but still pourable

Pour glaze over the top of the cake, spreading evenly over the sides

Chill until the glaze sets

Brush the top of the whole chestnuts with the edible gold dust (optional)

Arrange the chestnuts across top of cake

Serve at room temperature