Preheat the oven to 180C. Butter and line 2 x 20/21cm sandwich tins.
Using a hand held electric whisk or a stand mixer, cream the butter and sugar together until very light and fluffy – it should be almost mousse like.
Add the eggs one at a time with a tablespoon of the flour, mixing lightly between each addition, then add the remaining flour.
Add as much lemon juice as necessary to give a dropping consistency, then divide between 2 tins.
Bake in the oven for between 20-25 minutes until the sponge has shrunk away from the sides slightly, is springy to touch and a very light golden brown.
Leave to cool in the tins for at least 10 minutes, then turn out onto a cooling rack.
For the filling, put the blackberries in a bowl and sprinkle over the caster sugar and crème de mure if using.
Leave to marinade for a short while – they will give out some juices.
Whip the cream then fold in the icing sugar and spices – the cream needs to be just beyond the soft peak stage – then pile this onto one of the sponges.
Top with the blackberries and pour over any juices.
Place the remaining sponge on top.
Dust with icing sugar or caster sugar and serve.