• 2 1/2 sticks unsalted butter (1 1/4 cups), more for greasing pan
• 200 grams chocolate wafer cookies (to make about 3 cups crumbs)
• 55 grams light brown sugar (about 1/4 cup)
• 3 grams fine sea salt (about 1/2 teaspoon), plus a pinch
• 2 ripe bananas, mashed
• 2 large eggs
• 455 grams dark brown sugar (about 2 1/2 cups)
• 2 tablespoons dark rum or 1 teaspoon vanilla extract
• 130 grams all-purpose flour (about 1 cup)
• 80 grams toasted walnuts, chopped (about 1/2 cup)
• Flaky sea salt, for sprinkling (optional)

• Heat oven to 375 degrees. Line a 9-by-13-inch baking pan with parchment, and grease with butter.
• Melt 1 stick of butter in a saucepan over low heat or in microwave.
• Put the chocolate wafer cookies in the bowl of a food processor and process to make fine crumbs.
• Add the light brown sugar, melted butter and a pinch of salt. Process until the mixture is the consistency of damp sand. Dump the mixture into the pan and press it into an even layer.
• Bake for 7 to 10 minutes, or until the surface is firm. Remove the pan and set aside.
• Reduce oven heat to 350 degrees.
• In a large skillet over medium heat, melt 12 tablespoons butter, then let it cook until the foam subsides and butter turns a deep nut brown, about 5 minutes. Cool.
• In a large bowl, whisk together bananas, eggs, dark brown sugar and rum.
• Whisk in brown butter.
• In a separate bowl, whisk together flour and fine salt.
• Fold into batter along with the toasted walnuts. Pour the mixture over the prepared crust and spread evenly.
• Sprinkle top with flaky salt if using.
• Transfer pan to oven and bake until the top is firm and a toothpick inserted in the center emerges with a few crumbs attached (or clean) but not wet, 45 to 55 minutes. Cool completely on a wire rack; cut into 24 bars.

YIELD 24 bars

• NY Times