Preheat oven to 350 degrees F.
Melt chocolate (I use the microwave and it usually takes about 3 minutes).
Add the butter to melted chocolate and blend, slowly not to incorporate a lot of air.
In a separate large mixing bowl, whisk the eggs.
Add sugar to the eggs.
Pour the chocolate-butter mixture into the egg-sugar mixture.
Mix gently.
Add vanilla and flour; mix well.
Line a square baking pan with parchment paper.
Pour the brownie batter into the lined baking pan.
Bake for 40 minutes.
Cool before serving.