Preheat oven to 170°C and grease and line two 23cm round cake tins.
Beat egg yolks and caster sugar until fluffy, then mix in crème fraîche, zest, and flavoring.
Sift in chestnut flour and baking powder, then fold in stiff-peaked egg whites in three batches.
Pour batter into tins and bake for 23–30 minutes.
Simmer 250ml water and sugar for two minutes to make syrup.
Add citrus rind strips to syrup, simmer for three minutes, and cool.
Cool cakes in tins for five minutes before moving to a cooling rack.
Paint verbena leaves with egg white, coat in sugar, and dry in a low oven for 20 minutes.
Whisk softened butter for two minutes, then add icing sugar and lemon oil.
Add cream cheese and beat for five minutes until light and creamy.
Spread chestnut spread and lemon icing on both torte layers, leaving a 1cm gap at the edges.
Arrange clementine segments and pipe lemon icing rosettes on the bottom layer.
Top with the second layer and pipe further rosettes around the border.
Garnish with drained citrus rinds, remaining orange segments, and crystallised verbena leaves.