Step 1

Preheat the oven to 350°F (177°C). Line a large baking sheet with parchment paper.

Step 2

In the bowl of a stand mixer fitted with a paddle attachment, cream the butter, brown sugar, and granulated sugar on medium speed until they are smooth, about 1 minute.

Step 3

Add the vanilla and egg to the butter mixture and mix on medium speed until they are fully incorporated, scraping down the sides of the bowl as needed.

Step 4

In a medium bowl, whisk together the flour, cocoa powder, salt, baking powder, and baking soda. With the mixer on low speed, add the flour mixture in two batches to the butter mixture, and mix until the ingredients are just combined, about 1 minute.

Step 5

Add the dark chocolate and milk chocolate, and mix until they are just incorporated with the dough, about 30 seconds.

Step 6

Portion the dough into 10 dough balls of equal size and place them about 2 - 3 inches apart on the baking sheet. Top each dough ball with a big piece of white chocolate. I like using a sharp knife or vegetable peeler to get very thin, large pieces of white chocolate.

Step 7

Bake the cookies for 12 to 14 minutes, or until the cookies are caramelized along the edges and the centres are just set. The white chocolate should start to turn slightly golden.

Step 8

Remove cookies from oven and top each cookie with a sprinkling of the Maldon sea salt flakes. Allow the cookies to cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.