Line an 8 inch square metal pan with foil and spray foil with cooking spray or rub with a little extra butter. Set aside.
In a saucepan set over medium heat, melt the butter. Reduce heat to low, then add the chocolate and stir until melted. If pan is very hot, turn off heat and melt the chocolate over residual heat. Stir the brown sugar into the hot mixture. Set aside to cool for 10 minutes.
In a mixing bowl or bowl of stand mixer, beat the eggs on high for about 2 minutes. Beat in the salt and sugar; continue beating another minute or 2 minutes until light. Beat in the vanilla then gradually pour in the chocolate. With a heavy duty scraper (my favorite tool for mixing flour into brownies because it helps you incorporate flour without beating the batter too much), stir in the flour.
Pour into the pan and bake on center rack at 350 degrees F for 25-30 minutes. Remove from oven and let cool on a rack at room temperature for about 30 minutes, then transfer to the refrigerator and chill for about 2 hours.
Lift from pan by grasping foil. Set brownies on a cutting board and score into 12 or 16 bars. Stick a Circus Animal on each brownie. Circus Animals should adhere without any extra icing, but if for some reason your animals won't stick, melt a little chocolate in the microwave and use it as a glue.