Preheat the oven to 180°C/gas mark 4. Grease and line the bases of three 18cm cake tins.
Cream together the butter, spread and sugar for 5-7 minutes until light and fluffy. Gradually add the eggs, beating well between each addition. Add the clementine zest.
Sift in the flour and baking powder and add the ground almonds. Mix gently to just combine.
Divide the mixture between the cake tins and bake the cakes for 35 minutes, until golden and springy to the touch. Remove from the oven, then leave to cool in the tins for 5 minutes. Turn out on to wire racks and leave to cool completely.
While the cakes are cooling, make the candied clementines. Increase the oven temperature to 200°C/gas mark 6. Place the sugar and 200ml water in a medium saucepan over a low heat and stir to dissolve the sugar. Once the sugar has dissolved, increase the heat and bring to a simmer. Add the clementines and simmer for 5 minutes. Place them on a baking tray lined with parchment and bake in the oven for 10-12 minutes. Remove from the oven and leave to cool.
Combine the double cream, clementine juice and icing sugar in a medium bowl, then whisk to medium peaks.
Place one cake on a cake stand and spread a third of the cream on top. Place the second cake layer on top and repeat. Top with the third layer and spread on the remaining cream.
Place the candied clementines on top and toss over the toasted flaked almonds. Scatter over sprigs of herbs to decorate.