Dissolve sugar in 100ml water and boil in a large saucepan until it becomes a golden caramel.
Stir in double cream, let cool, and chill until set.
Whisk softened butter until fluffy and gradually incorporate the chilled caramel mixture.
Preheat oven to 180°C and mark six 20cm and six 15cm circles on baking parchment.
Whisk eggs and caster sugar until light, foamy, and the whisk leaves a trail.
Fold in the flour and spread the batter evenly across the 12 marked circles.
Bake for 8-10 minutes until golden, then trim the edges and cool on a wire rack.
Spread flaked almonds on parchment paper.
Insert cocktail sticks into each hazelnut.
Boil sugar in 8 tablespoons of water to a deep golden syrup and pour half over the almonds.
Dip hazelnuts into the remaining hot caramel and leave to set upright.
Coat one 15cm sponge circle with the remaining caramel.
Cut the caramel-topped sponge into eight wedges while still slightly soft using an oiled knife.
Stack and sandwich the six 20cm sponges with buttercream, coating the top and sides.
Stack five 15cm sponges with buttercream and place them on top of the larger tier.
Press crushed almond praline into the sides of both cake tiers.
Pipe 16 buttercream rosettes on the lower tier and top each with a caramel hazelnut.
Pipe eight rosettes on the top tier and lean the caramel sponge wedges against them.