Melt the chocolate and the butter together.
In a bowl, beat the cheese and sugar until smooth, then beat in the eggs, vanilla and almonds.
Stir in the chocolate/butter mixture, followed by the flour and baking powder.
Spoon into muffin cases or a deep, round, buttered tart tin, filling just short of the top.
Sprinkle with toasted almonds or pine nuts and bake at 190C (170C fan-assisted)/375F/gas mark 5 for about 25 minutes for muffins.
For the tart, bake until the middle has gently risen, which will take a little longer.
Beat the sugar, zest and cheese until utterly smooth, then whisk in the eggs and crème fraîche.
Stir in the lemon juice, then leave the mixture to sit for 30 minutes.
Check the tart case for any cracks or holes and patch them up.
Heat the oven to 170C (150C fan-assisted)/335F/gas mark 3.
Pour in the filling through a sieve to remove the zest and bake for 25-30 minutes, until barely set.
