Preheat the oven to 350ºF (180ºC). Lightly spray a brownie pan with baking spray and line it with parchment paper. Set aside.
Place the butter and dark chocolate callets in a heat-safe glass measuring cup or bowl.
Melt the butter and chocolate in the microwave for 1 to 2 minutes (length of time is dependent on the power of your microwave).
Stir the melted butter and chocolate together until smooth. Set aside.
Whisk together the flour, cocoa powder, and salt in a small bowl until well combined. Set aside.
Use a hand mixer to mix the sugars, eggs, and vanilla until thick and creamy, about 1 to 2 minutes.
Pour the melted butter-chocolate mixture into the egg mixture and continue to mix until no streaks of egg remain.
Add the flour mixture to the bowl.
Switch to a rubber spatula or wooden spoon and gently fold the wet and dry ingredients until the flour is just mixed in. It will seem like it takes a while, however it will mix in!
Pour the batter into the prepared pan. It should settle into the pan on its own, however, you can smooth it into an even layer if needed.
Place the pan in the preheated oven and bake the brownies for 15 to 16 minutes.
Carefully remove the pan from the oven and set it on a wire cooling rack. Sprinkle the Easter candy evenly across the top of the brownies.
Return the pan to the oven and bake the brownies for 2 to 3 minutes more.
Remove the pan from the oven and set it back on the wire rack to cool completely before slicing and serving.