Preheat the oven to 350 F. Line your baking tray with parchment paper; set aside.
Mix flour, cocoa powder, baking powder and salt in a large bowl. Keep it aside.
Add the butter, sugar, and vanilla extract in a large bowl and beat it at medium speed, scraping down the sides for at least 2-3 mins or until the mixture is creamy.
Add in the eggs one at a time and beat on medium until everything is incorporated well.
Add the flour mixture to the butter mixture in batches and mix it well.
Wrap the dough with a cling wrap and refrigerate for at least an hour.
Once chilled, roll out a tbsp of dough in between your palms, and flatten it a bit. Use the back of a wooden spoon or your thumb to make an indent in the centre of the cookie and place it on the prepared try. Repeat with rest of the dough.
Refrigerate for another 20-30 mins.
Bake for at least 12-13 mins in a preheated oven. Let the cookies cool for 5 minutes in the baking tray before transferring them to a wire rack to cool completely.
Chocolate Ganache
Start by chopping the chocolate bars into small pieces and keeping them aside in a heat-safe bowl.
Warm the heavy cream in a saucepan over low heat, stirring occasionally, until it starts to simmer.
Pour the warm cream over the chopped chocolate and let it rest for 4-5 minutes to allow the chocolate to melt. Gently mix the cream and chocolate using a spatula until they are properly combined and smooth.
Spoon the ganache into the indents. Garnish with some shaved chocolate or other toppings, if desired.