Preparation

1. For the banana crunch mix-in: Preheat the oven to 121°C (250°F) and line a rimmed baking sheet with parchment paper or nonstick liner. Combine the powdered milk, flour, cornflakes, cornstarch, sugar, and salt in a medium bowl and stir vigorously with a whisk until all the ingredients are evenly distributed. Drizzle the melted butter over the dry ingredients and toss until clumps start to form.

2. Pour into the lined baking sheet and spread into an even layer. Bake for 10 minutes. Stir the crunch with a spatula, making sure the darker outer clumps get mixed with the inner clumps, and then bake for about 10 minutes more. Break up any big chunks and let cool completely on the baking sheet.

3. While the crunch is baking, put the freeze-dried bananas in a food processor and pulse until they are reduced to powder. Chop the white chocolate into small chunks and place them in a microwave-safe bowl. Microwave for 30 seconds, then stop and stir. Cook for another 30 seconds, and then stir until melted and smooth, letting the residual heat from the bowl finish melting the white chocolate. If there are any stubborn big pieces, microwave in 10-second intervals and stir until completely melted and smooth. Be careful of overheating, though, as white chocolate has a tendency to scorch easily.

4. Once the crunch has cooled, pour it into a bowl and add the banana powder. Drizzle the white chocolate over the bowl and toss until the crunch absorbs the white chocolate and banana powder. Refrigerate while you make the brownie batter.

5. For the brownie batter: Increase the oven temperature to 177°C (350°F). Coat a 23 x 33 cm (9 x 13-inch) baking pan with cooking spray and then line the bottom and sides with parchment paper, with 5 cm (2 inches) of paper overhanging the edge of the pan on two sides. Place 115 grams (4 ounces) of the chopped chocolate in a large heatproof mixing bowl. Place the butter in a medium skillet and turn the heat to medium-high. Cook the butter, stirring constantly, until it has completely melted and the solid butterfat starts to brown. Turn the heat off and continue to stir until the heat browns all the butterfat and it smells fragrant and nutty. It should be bordering on reddish brown. Immediately pour the hot butter into the bowl with the chopped chocolate, making sure to scrape out all the brown bits in the pan. Stir the chocolate until it melts. Add the cocoa and salt and stir until the cocoa has been absorbed. Add the beer and stir to incorporate.

6. Combine the eggs, banana, both sugars, baking powder, and vanilla in the bowl of a stand mixer fitted with a paddle attachment. Beat the ingredients together on medium speed until they are combined and thick, about 30 seconds. Add the chocolate-beer mixture and mix on medium-low speed until incorporated. Add the flour and beat on medium speed until absorbed into the batter, about 15 seconds. Remove the bowl from the stand mixer, add the remaining 110 grams (3.8 ounces) chocolate and half the banana crunch mix-in, and fold them in using a large spatula.

7. Pour the batter into the lined baking pan and spread evenly. Cover with aluminum foil and bake until a toothpick inserted in the center comes out clean, 35 to 40 minutes. Let cool completely on a wire rack.

8. For the chocolate-beer ganache: Chop the chocolate into .6 cm (1/4-inch) chunks. Place the chocolate and butter in a microwave-safe bowl and microwave for 30 seconds. Stir and then cook for 1 minute, stopping after 30 seconds to stir again. Stir until completely smooth. If there are any stubborn big pieces, microwave in 15-second intervals and stir until completely melted and smooth. Add the cream and beer to the warm chocolate and stir until incorporated. Spread the ganache over the cooled brownies and sprinkle the reserved banana crunch mix-in and the sea salt over the ganache. Let cool completely before cutting and serving.