Preheat oven to 350°F. Prepare your baking pan by lining with parchment paper and spray or butter to avoid sticking.
In a medium-sized bowl, whisk together all purpose flour, cocoa powder, salt, and espresso powder. Set aside.
In a microwaveable bowl, add the Kinder Milk chocolate and unsalted butter. Microwave in 20-30 second intervals, stirring in between. It should take about 2-3 rounds before it all melts when you stir. Set aside to cool a bit.
In another bowl, add the eggs, sugar, and vanilla extract. Whisk for a good minute just until it starts to lighten in color a bit.
Add the dry ingredients and the melted butter and chocolate mixture into the egg mixture. Use a rubber spatula to mix without incorporating air bubbles.
Add both chopped chocolates in and give it another stir.
Pour the batter into the prepared baking pan and pop in the oven for 22 minutes.
Once the brownies are done, take them out and let them cool before cutting and serving.