1. Whisk together milk, egg and vanilla in a jug. Combine flour, sugar and bicarbonate of soda in a bowl. Make a well in centre. Add milk mixture and whisk until combined.
2. Transfer a third of the mixture to a second bowl. Add cocoa and whisk until combined. Pour cocoa mixture into a squeeze bottle.
3. Heat a medium non-stick frying pan over medium heat. Brush pan with butter. Draw a web pattern with the cocoa mixture into the pan. When nearly set, ladle plain mixture over the top to completely cover. Cook for about 3 minutes or until bubbles appear on surface. Turn over and cook other side for two minutes or until cooked through.
4. Transfer to a plate. Top with yoghurt and berries. Repeat, brushing pan with butter between pancakes.