Preheat the oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper, leaving some overhang for easy removal; set the pan aside.

Make the base: In a large bowl, whisk together 3/4 cup (170.25 g) melted unsalted butter, 1/2 cup (100 g) granulated sugar, and 2 eggs until smooth.

Add 2 1/2 cups (210 g) graham cracker crumbs, 3/4 cup (67.5 g) shredded sweetened coconut, and 1/3 cup (28.67 g) cocoa powder to the butter mixture. Stir with a large spoon until completely combined.

Transfer the mixture to the prepared pan. Press it into an even layer across the bottom of the pan (the mixture will be sticky—wet your fingers slightly if needed). Bake for 12 to 15 minutes, until the surface is firm and no longer shiny.

Remove the pan from the oven and transfer to a cooling rack. Cool the base completely in the pan before adding the filling.

Make the filling: In a microwave-safe bowl, combine 1 1/4 cups (322.5 g) creamy peanut butter and 1/3 cup (75.67 g) unsalted butter. Microwave in short bursts, stirring between bursts, until the mixture is completely melted and smooth.

Whisk in 3 cups (360 g) powdered sugar in three additions (about 1 cup at a time). Add 1/3 cup (81.33 ml) milk in two roughly equal additions between the sugar additions—i.e., sugar, half the milk, sugar, remaining milk, final sugar—whisking until the filling is smooth and spreadable.

Spread the filling evenly over the cooled base. Refrigerate the pan until the filling is firm, about 1 hour.

Make the topping: In a heatproof bowl set over simmering water (double boiler) or in the microwave at 50% power in short bursts, melt 8 ounces (226.8 g) semisweet chocolate with 2 tablespoons unsalted butter, stirring until smooth.

Pour and spread the melted chocolate evenly over the chilled filling. Let the topping set at room temperature, or refrigerate to speed up setting.

Once the topping is set, use the parchment overhang to lift the slab from the pan. Cut into bars. Store leftovers in an airtight container at room temperature or in the refrigerator.