Preheat the oven to 190°C. Line a standard muffin tin with 6 paper cases*.
Sift the flour and baking powder together.
Cream the butter with the remaining 85 g sugar. Beat the egg and vanilla with a fork, then beat into the creamed mixture.
Add 1/3 of the flour & baking powder mix, then follow with 1/2 the milk and repeat, then fold in the last 1/3 of the flour & baking powder.
Wash the blackcurrants well, removing any leaves and stalks if handpicked. Dry well on kitchen roll.
Spoon half the cake mixture into the paper cases (approx. a heaped tsp of mixture into each one). Spoon the blackcurrants on top, dividing equally amongst the cases, then sprinkle over a teaspoon of caster sugar.
Spoon the rest of cake mixture on top of the fruit, then finish with a little extra sugar.
Bake for 20 minutes. Remove from the oven and leave to cool on a wire rack for at 15 minutes then enjoy warm or leave to cool completely.
* I use 'tulip cases'. If using standard paper cases, you may get 7 cakes rather than 6.
You could also make it in a 15-16 cm cake tin and bake for 25-30 minutes.
Works equally well with blackberries.