Preheat the oven to 350°F. Line a 9×13-inch baking pan with parchment paper, leaving an overhang on the long sides.
Make the topping: In a medium saucepan over medium heat, combine the butter, brown sugar, evaporated milk, and beaten egg yolks. Cook, stirring constantly, for 10 to 12 minutes until the mixture thickens and coats the back of a spoon.
Remove the topping from heat and stir in the vanilla, shredded coconut, and chopped pecans. Set aside to cool for 10 minutes.
Make the cookie base: In a large mixing bowl, whisk together the melted butter, granulated sugar, and brown sugar until well combined.
Add the eggs one at a time, whisking after each one. Stir in the vanilla extract.
Add the flour, cocoa powder, baking powder, and salt. Stir until just combined. Fold in the chocolate chips.
Press the chocolate dough evenly into the prepared pan, spreading it to all four corners.
Spoon the cooled coconut pecan topping over the base and spread it gently to the edges.
Bake for 28 to 32 minutes, until the edges are set and the topping is golden brown. The center will look slightly underdone — that's correct.
Cool completely in the pan for at least 2 hours before lifting out and cutting into bars.