Pre-heat the oven to 180°C. Line a 12 hole cupcake tin with cupcake cases. Place the butter, sugar, self-raising flour, black treacle, Golden Syrup, eggs and vanilla extract in a large mixing bowl. Whisk together using an electric hand-held whisk until smooth; usually 1-2 minutes. Fold in 50g of the finely chopped pistachios. Spoon into the cupcake cases and bake for 18-22 minutes until risen and springy to the touch. Remove and allow to cool on wire racks. Once the cupcakes are cool, decorate the tops with a tablespoon of finely chopped pistachios. Place the white chocolate in a heatproof bowl and microwave in 10 second intervals, stirring in between checking, until you have smooth, melted white chocolate. Use a spoon to drizzle the white chocolate across the tops of the pistachios on the top of the cupcakes.
