For the Cookies: Preheat your oven to 350°F (177°C) and line several baking sheets with parchment paper. In a stand mixer fitted with the paddle attachment, cream together the brown sugar, granulated sugar, butter, and vanilla on medium speed for 4 to 5 minutes, or until the mixture becomes light in color and fluffy in texture.
Add the eggs one at a time, ensuring the first is fully incorporated before adding the second. Then add the baking powder, baking soda, and salt, mixing on medium speed for about one more minute until well combined. Remove the bowl from the mixer.
Next, add the flour and mix just until barely combined—you should still see some streaks of flour. Scrape the sides and bottom of the bowl to make sure everything is evenly mixed. Fold in the chopped dark chocolate and chopped hard caramel pieces until evenly distributed throughout the dough.
Using a tablespoon or cookie scoop, portion 2-tablespoon-sized dough balls onto the prepared baking sheets, spacing them about 2 inches (5 cm) apart. Bake one sheet at a time in the center of the oven for about 11 minutes. Remove the cookies and gently nudge them back into round shapes using the edge of a silicone spatula. Return the cookies to the oven for one more minute. They will appear slightly underbaked in the center.
Allow the cookies to cool on the baking sheet for 10 minutes before transferring the warm cookies to a wire rack to cool completely. If desired, sprinkle with flaky sea salt before serving.