Chop chocolate. Combine half of it with butter, and melt together in the microwave, or over low heat on the stove.
When melted and smooth, remove from heat and cool while you continue with the recipe.
Whisk eggs and granulated sugar together until light yellow and frothy. Add vanilla extract into the eggs.
Pour cooled chocolate into the eggs, and whisk until glossy and smooth.
Set a wire strainer over the bowl, and sift flour, cocoa, baking powder, and salt on top. Gently stir until just combined.
Stir chopped chocolate into the brownie batter.
Spread batter in lined pan, and bake until shiny and crackly on top. Let brownies cool completely.
Make the frosting by melting butter. Add cocoa powder to warm butter, and whisk until smooth, glossy, & free of lumps.
Whisk in salt, vanilla, and milk. Then add sifted powdered sugar. Blend until smooth and shiny.
Spread frosting on top of baked and cooled brownies. The frosting will firm up as it cools down.
Top with chocolate eggs or Easter sprinkles. Let the frosting set before serving.