Preheat your oven to 350°F (180°C) and line a 9x9 inch baking pan with parchment paper, leaving some overhang on the sides for easy removal.
In a heatproof bowl, melt the butter and dark chocolate together using a microwave or a double boiler until smooth. Allow to cool slightly.
In a separate large bowl, whisk the sugar, eggs, and vanilla extract until well combined and fluffy (mousse-like).
Gradually pour the cooled melted chocolate mixture into the egg mixture, and whisk constantly until smooth and well combined.
Sift in the flour, cocoa powder, and salt into the wet ingredients. Gently fold the dry ingredients into the wet until just combined. Be careful not to overmix.
Pour the brownie batter into the prepared baking pan and spread it out evenly.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs (but not wet batter). Don’t overbake them if you want fudgy brownies.
Place the halved creme eggs on top of the brownie and carefully press them in.
Allow the brownies to cool completely in the pan before slicing and serving.