Step 1: Preheat your oven to 350°F (175°C). Line a 9×13 inch baking pan with parchment paper, leaving an overhang on the sides. Lightly grease the parchment paper.
Step 2: In a large microwave-safe bowl or a heatproof bowl set over a saucepan of simmering water (double boiler method), combine the unsalted butter and unsweetened chocolate. Melt gently, stirring occasionally, until smooth and fully combined. Remove from heat and let cool slightly.
Step 3: In a separate large bowl, whisk together the granulated sugar, brown sugar, and eggs until light and fluffy, about 2-3 minutes. Add the vanilla extract and mix well.
Step 4: Pour the slightly cooled chocolate mixture into the egg mixture and stir until just combined. In a medium bowl, whisk together the all-purpose flour, Dutch-processed cocoa powder, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing only until no streaks of flour remain.
Step 5: Pour the brownie batter into the prepared 9×13 inch pan and spread evenly. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with moist crumbs, but not wet batter. Let the brownie cool completely in the pan on a wire rack before proceeding.
Step 6: In a large mixing bowl, beat the softened cream cheese and unsalted butter together until smooth and creamy. This will take 2-3 minutes on medium speed with an electric mixer.
Step 7: Gradually add the confectioners’ sugar, 1 cup at a time, beating until fully incorporated and smooth after each addition.
Step 8: Add the pure mint extract and a few drops of green food coloring (if desired) to achieve that signature minty hue. Beat until the color is even and the mint flavor is well distributed. Taste and adjust mint extract if needed.
Step 9: Once the brownie base is completely cool, spread the mint cream cheese mixture evenly over the top. Use an offset spatula for a perfectly smooth finish. Place the pan in the refrigerator for at least 30 minutes to allow the mint layer to set firmly.
Step 10: In a microwave-safe bowl, combine the semi-sweet chocolate chips (or chopped chocolate) and the shortening (or coconut oil). Microwave in 30-second intervals, stirring well after each, until the chocolate is fully melted and smooth.
Step 11: Quickly fold in the crispy rice cereal into the melted chocolate. Work fast, as the chocolate will start to set. The goal is to coat all the cereal evenly.
Step 12: Remove the pan from the refrigerator. Quickly and evenly spread the chocolate-cereal mixture over the chilled mint layer. Work swiftly before the chocolate sets too much. Return the pan to the refrigerator for at least 1-2 hours, or until the chocolate topping is completely firm.
Step 13: Once fully chilled and firm, use the parchment paper overhang to lift the entire slab of mint chocolate crunch brownie bars out of the pan and onto a cutting board. Use a sharp, hot knife (run under hot water and wipe dry) to cut into squares or rectangles. Clean the knife after each cut for the cleanest slices. Serve chilled or at room temperature.