In a large bowl, sift together the dry ingredients: all-purpose flour, unsweetened cocoa powder, baking soda, and salt.
In a bowl of a stand mixer, cream the unsalted butter with granulated sugar until smooth and creamy. About 2 minutes.
Add eggs and vanilla extract, and beat again for 1 minute.
Add the dry ingredients to the wet ingredients, and mix again until just combined.
Then add the buttermilk or plain yogurt and mix again until just combined.
Fold in the chopped semi-sweet chocolate bar, cover the bowl, and chill the dough for 30 minutes.
Use a medium cookie scoop, scoop out dough balls and flatten into disks.
Wrap the cookie dough around each soft caramel, and chill again for 15 minutes.
Meanwhile, preheat oven to 350°F (180°C), then place the chilled cookies on a cookie sheet lined with parchment paper or silpat about 2 inches apart.
Bake for 10-12 minutes, rotating the pan halfway through.
Sprinkle the cookies with flaky sea salt right after you remove them from the oven.
Cool on the cookie sheet for 10 minutes, then transfer to a wire rack to cool completely.