Preheat your oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper, letting some overhang on the long sides to create a sling, and lightly spray with nonstick cooking spray.
nonstick cooking spray, parchment paper
In a large mixing bowl, whisk together the melted and slightly cooled unsalted butter and granulated sugar for 30–60 seconds until combined and a little glossy. Add the eggs and vanilla extract and whisk again until the mixture is smooth and slightly thick.
1 cup unsalted butter, 1 3/4 cups granulated sugar, 3 large eggs, 2 teaspoons pure vanilla extract
In a separate bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking powder, and fine sea salt until evenly combined and no streaks of cocoa remain.
1 cup all-purpose flour, 3/4 cup unsweetened cocoa powder, 1/2 teaspoon baking powder, 1/2 teaspoon fine sea salt
Gently add the dry mixture into the wet mixture, stirring with a spatula just until no dry flour is visible. The batter will be thick, like brownie batter. Fold in the chopped German’s sweet chocolate or semi-sweet chocolate chips, if using. Scrape the batter into the prepared pan and spread it evenly to the corners.
1/2 cup chopped German’s sweet chocolate or semi-sweet chocolate chips
Bake the chocolate layer at 350°F (175°C) for 18–22 minutes, until the top looks set and a toothpick inserted near the center comes out with a few moist crumbs (not wet batter). Do not overbake, as it will go back in the oven with the topping. Place the pan on a cooling rack while you prepare the topping; the base can be warm but not piping hot when you add the frosting.
In a medium saucepan, whisk together the evaporated milk, granulated sugar, light brown sugar, and egg yolks until smooth.
1 cup evaporated milk, 3/4 cup granulated sugar, 3/4 cup light brown sugar, 3 large egg yolks
Add the pieces of unsalted butter to the saucepan and cook over medium heat, whisking almost constantly, until the mixture thickens and coats the back of a spoon, about 8–10 minutes. It should look like a loose pudding; do not let it boil hard to avoid scrambling the eggs.
1/2 cup unsalted butter
Remove the saucepan from the heat and stir in the vanilla extract, sweetened shredded coconut, chopped pecans, and a pinch of salt. The mixture will thicken more as it cools; if it seems very runny, let it sit for about 5 minutes.
1 teaspoon pure vanilla extract, 1 1/2 cups sweetened shredded coconut, 1 1/2 cups pecans, salt
Spoon the warm coconut pecan topping over the slightly cooled chocolate bar base and spread it evenly to the edges. A little texture on top is fine and looks rustic.
Return the pan to the oven and bake at 350°F (175°C) for 12–15 minutes, just until the topping is set and lightly bubbling around the edges.
Set the pan on a wire rack and let the bars cool completely, about 1½–2 hours at room temperature. For faster cooling, let the pan cool on the counter for 30 minutes, then chill in the refrigerator until set. Use the parchment sling to lift the slab from the pan, then cut into 24–30 bars with a sharp knife, wiping the blade between cuts for clean edges. Serve at room temperature.