In a large mixing bowl, whisk together the all-purpose flour, Dutch-processed cocoa powder, baking powder, baking soda, and salt until evenly combined.

Using a stand mixer, cream together the unsalted butter, light brown sugar, and granulated sugar on medium speed for about 3-4 minutes until light and fluffy. Add in the egg, egg yolk, vanilla extract, and oil, mixing for another minute.

Gradually add the dry ingredients into the wet mixture, mixing on low speed just until combined.

Wrap the dough in plastic wrap and refrigerate it for at least 5 hours, or ideally overnight.

Preheat your oven to 180°C (350°F). Line two baking sheets with parchment paper.

Once the dough is chilled, scoop out small portions (about 10 grams each) and roll them into balls. Coat each ball thoroughly in turbinado sugar.

Bake the cookies in the preheated oven for 7-8 minutes, until the edges are set but the centers remain soft.

In a medium saucepan, melt the granulated sugar over medium heat, stirring continuously until it turns into a smooth, amber liquid. Remove from heat, whisk in the unsalted butter and heavy cream.

Take one cooled cookie and spread a generous amount of the salted caramel filling on the flat side. Top it with another cookie, pressing down gently.