Preheat the oven to 190°C. Line a large baking sheet with baking paper.
Sift the flour, cocoa, baking powder and sugar into a mixing bowl.
Add the butter and rub in until it resembles fine crumbs. Add 75g of the white chocolate drops and 75g of the milk chocolate drops and mix briefly to distribute them evenly.
Make a well in the centre of the mixture, add the eggs and vanilla essence and then gradually pour in the milk; add just enough milk to make a damp dough – it should not be wet or sloppy.
Turn out onto a lightly floured surface and roll out to about 4cm thick. Stamp out using an 8cm round fluted cutter and place on the baking sheet. Gently knead the trimmings together, re-roll and stamp out more rounds. Brush the tops with milk.
Bake for 16–18 minutes until springy to the touch. Transfer to a wire rack to cool.
Melt the remaining white and milk chocolate drops and drizzle over the scones.
National Trust Book of Scones by Sarah Clelland (National Trust Books) - £9.99 - available at shop.nationaltrust.org.uk (ACE Best Product Award winner)
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