Lightly grease a 12-hole deep muffin tin. Cut out 12 strips of baking parchment, each about 1.5cm wide. Cut each strip in half, then lay inside each muffin hole to make a cross. Trim the ends so they rise about 1cm above the rim of the holes. You'll use these as handles to remove the cakes when they are cooked.
Heat oven to 180C/160C fan/gas 4. Beat together the butter and sugar until pale and creamy. Beat in the eggs, a little at a time, then add the lemon zest and half the juice. Mix together well, then stir in half the flour. Stir in the remaining lemon juice, then the remaining flour.
Spoon the cake mixture into the tins, about 1 heaped tbsp per case, then smooth over with the back of a spoon. Sprinkle a couple of blueberries over each cake, then bake for 10 mins.
To make the topping, whisk together the soured cream, icing sugar, egg and vanilla extract until smooth. Take the cakes out of the oven - they should be pale and just firm. Gently press down to make a flat top, then spoon some cheesecake topping over each cake - the holes should be filled almost to the top. Scatter over some more blueberries. Return to the oven and bake for 5-7 mins more until the topping is just set and gives only a little wobble when tapped.
Leave the cakes to cool in the tin, then gently ease away from the sides of the tin and lift out using the paper handles.