Preheat the oven to 350°F (175°C). Grease a 9x13 inch baking pan with butter or cooking spray.

In a medium saucepan, melt the butter and unsweetened chocolate over low heat, stirring occasionally, until smooth.

Remove the saucepan from the heat and stir in the sugar until well combined.

In a separate bowl, whisk together the flour, baking powder, and salt.

Add the flour mixture to the chocolate mixture and stir until just combined.

Add the eggs, one at a time, stirring well after each addition.

Stir in the vanilla extract.

Pour the batter into the prepared baking pan and smooth out the surface with a spatula.

Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

Let the brownies cool completely in the pan on a wire rack before cutting into squares and serving.