Preheat your oven to 350°F (175°C) and grease an 8×8-inch baking pan or line it with parchment paper.

In a double boiler or microwave-safe bowl, combine semisweet chocolate and unsalted butter. Heat gently until melted and smooth.

Gradually whisk in large eggs, one at a time, ensuring each is fully blended into the mix before adding the next.

In a separate bowl, sift together the all-purpose flour, cocoa powder, and salt. Gradually fold this dry mixture into the wet ingredients.

Pour your brownie batter evenly into the prepared 8×8-inch pan, smoothing the top with a spatula. Bake for 20-25 minutes.

Once baked, remove the brownies from the oven and let them cool in the pan on a wire rack for about 30-45 minutes.

Heat the heavy whipping cream in a saucepan until just simmering. Pour over chopped semisweet chocolate and let it sit before stirring.

Carefully lift the cooled brownies out and cut into squares or rectangles. Dip into the ganache to coat.

Sprinkle a pinch of fleur de sel on each Petit Four while the ganache is still wet. Allow to set completely at room temperature.