Layered Chocolate Brownie Bars

For the brownies:

Adjust an oven rack to the lower-middle position. Preheat the oven to 350°F. Grease an 8 by 8-inch baking pan and line a parchment sling (a 9 by 9-inch pan will work, too).

In a medium saucepan over medium-low heat, melt the butter and the bittersweet chocolate until both are melted and smooth. Remove from the heat and add the cocoa powder, stirring until smooth. Set aside to cool slightly.

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

In a large bowl, whisk the eggs, oil, sugars, and vanilla. Add the slightly cooled chocolate mixture and whisk until smooth. Add the flour mixture and stir with a spatula until just combined.

Pour the batter into the prepared pan and bake 22 to 27 minutes, until the sides of the brownies have set, the top is beginning to crackle and look glossy, and a wooden skewer or toothpick inserted into the center comes out with crumbs. The batter on the skewer should not be wet, but should have a good amount of crumbs clinging to it. Transfer the pan to a wire rack and let cool completely. Place in the refrigerator and chill for an hour.

For the filling:

In the bowl of a stand mixer fitted with a paddle, beat the butter on medium until creamy. Scrape down the sides and add the vanilla, mint, and salt. Mix on low until combined and then beat on medium for 1 minute.

Turn the mixer to low and slowly add the confectioner‘s sugar, a little at a time, mixing until combined, and stopping to scrape down the sides of the bowl as necessary. Increase speed to medium-high and beat 6-8 minutes until light and fluffy.

For the ganache:

Place the chocolate in a small bowl. Heat the heavy cream in a small saucepan until it is simmering and just about to boil. Pour the cream over the chocolate, cover the bowl with plastic wrap, and let sit for 5 minutes. Remove the plastic and whisk until completely smooth. Let cool to room temperature before using.

To assemble the bars:

Spread the mint filling evenly across the chilled brownies. Return the pan back to the fridge and chill for 1 hour.

When the filling has chilled, pour the cooled ganache over the top, and using an offset spatula, spread the ganache in an even layer (decorate with edible rose petals and cacao nibs, if desired). Put the pan back in the fridge for 1 hour. Remove the pan from the fridge, and wait 10 minutes before cutting, to allow the glaze to soften slightly. Cut the squares and serve.