1. Heat the oven to 350 F.
  2. Grease a square baking pan with butter or line it with 2 overlapping pieces of parchment paper or aluminum foil and grease the lining.
  3. Combine the stick of butter and the chocolate in a saucepan over very low heat, stirring occasionally.
  4. When the chocolate is melted, remove the saucepan from the heat and continue to stir until the mixture is smooth.
  5. Transfer the mixture to a bowl and stir in the sugar.
  6. Beat in the eggs, one at a time.
  7. Stir in the flour, salt, and the vanilla.
  8. Pour and scrape the mixture into the prepared pan and bake for 20 to 25 minutes, until just barely set in the middle.
  9. Cool.
  10. Remove the brownies.
  11. If not, cut them in squares right in the pan.
  12. Store, covered, at room temperature, for no more than a day.