Put the two sugars in a large mixing bowl and set aside. Add the butter and milk powder to a small saucepan, place over a medium heat and cook until browned, stirring constantly to prevent the milk powder from catching on the bottom of the pan. Once you can see brown flecks in the butter and it has a nutty aroma, pour over the sugars and stir together with a whisk. Leave to cool for a couple minutes, then add the egg yolk, milk and vanilla and whisk until smooth. Add the flour, salt, baking powder and bicarbonate of soda and stir together with a spatula to form a dough. Add the chocolate and stir to distribute. Cover and refrigerate the dough for an hour before baking.

Preheat the oven to 180°C/160°C Fan (350˚F) and line a large baking tray (pan) with baking parchment.

Divide the dough into six equally sized pieces and roll into balls. Place on the prepared tray and sprinkle with a little flaked sea salt. Bake for 12–13 minutes until lightly browned around the edges. Remove and set aside to cool on the tray for 5 minutes before carefully transferring to a wire rack to cool completely.

To decorate, dip the cookies halfway into the melted chocolate, allowing any excess to drip back into the bowl. Place the cookies back on the parchment-lined tray and refrigerate just until the chocolate has set.

Stored in a sealed container, the cookies will keep for 3–4 days.

Caramelised white chocolate

Oven method: This method works well but is on the slow side. The most important part of the process is to make sure you thoroughly stir the chocolate as it cooks and to continue cooking it until it reaches a deep golden colour. I prefer to use a minimum of 300g (10½ oz) white chocolate. You can use less, but this amount means it heats more evenly and is less prone to scorching.

Preheat the oven to 120°C (250°F). Roughly chop the chocolate and spread in an even layer across a rimmed baking tray (sheet pan). Place the tray in the oven and leave for 10–15 minutes. Remove the tray from the oven and stir and spread it with a spatula. Continue cooking the chocolate for around an hour in total, stirring every 10 minutes until the white chocolate has become deep golden brown, almost the colour of dulce de leche. Once the chocolate is caramelised, I like to stir through a pinch of sea salt to elevate the caramelised flavour.

Pour the finished chocolate onto a separate baking tray lined with baking parchment and spread in an even layer. Place in the refrigerator until fully set, then break into shards and store in a dark cool place in a sealed container.

Note: When you remove the chocolate from the oven to give it a stir, you may find it has become stiff and grainy. Before you return it to the oven, make sure to stir it until the mixture becomes smooth again. If lumps remain, the finished chocolate can have an unpleasant texture.

Microwave method: This method is quicker, but it is also more hands-on and requires more frequent stirring. It is also my preferred method when only a small amount of the chocolate is required.

Put the chocolate in a heatproof bowl and place in the microwave. Heat in short, 45 second bursts, stirring very well between each blast of heat. Repeat this process until the chocolate looks a little crumbly and has started to take on some colour. At this point repeat this process, using shorter 20-second bursts of heat, until the chocolate has reached the desired level of caramelisation, finishing with a little salt. This entire process can take up to 15 minutes.

Pour the finished chocolate onto a baking tray (sheet pan) lined with baking parchment and spread in an even layer. Place in the refrigerator until fully set, then break into shards and store in a dark cool place in a sealed container.

Note: As with the oven method, the texture of the chocolate will change as it is heated, so make sure to stir vigorously, until smooth, after every blast of heat. Take care not to leave the chocolate in the microwave for too long as it can overheat and become scorched very easily.