Preheat oven to 350F (180C).

Line an 8-inch baking dish with aluminum foil and spray with non-stick cooking spray.

In a small bowl, melt chopped unsweetened chocolate and cut-up unsalted butter, either over simmering water or in the microwave, stirring occasionally.

Cool the melted chocolate mixture slightly.

In a medium bowl, whisk together sugar, baking powder, salt, eggs, and vanilla extract.

Whisk the cooled chocolate mixture into the egg mixture until smooth.

Stir in all-purpose flour until no streaks of flour remain.

Scrape brownie batter into the prepared foil-lined pan and spread evenly with a spatula.

Bake in the preheated oven until a toothpick inserted halfway between the edge and center of the pan comes out clean, about 20 to 25 minutes.

Using the foil, lift the brownies from the pan to a cutting board.

Remove the foil by sliding it out.

Cut the brownies into 2-inch squares.

Store in an airtight container for several days.