Sift the flour, cocoa powder and baking powder into a large bowl and stir in the sugar. Make a well in the centre and gradually whisk in the egg and a little of the milk to form a thick batter. Stir in the remaining milk.
Heat a large nonstick frying pan over a medium heat. Using a scrunched up piece of kitchen paper, dip into the oil and use to wipe over the pan. Drop dessertspoons of the batter into the pan, spacing them well apart.
Cook for 1 minute, then scatter a little of the chopped chocolate over each. Cook for a further 1–2 minutes until bubbles start to appear on the surface and pop, then flip over and cook for a further 1–2 minutes until just firm. Remove from the pan and keep warm.
Repeat with the remaining batter to make about 28 blinis, adding more oil if necessary. Serve warm, topped with crème fraîche and raspberries.