Preheat the oven to 350 degrees. Coat an 8-inch square baking pan heavily with vegetable oil spray. Line the pan with an oversized sheet of parchment paper, leaving a 2-inch overhang on the sides for a built-in sling. Spray the parchment as well.

In a heat-proof glass bowl set over a small saucepan of gently simmering water, combine the butter and the chopped dark chocolate. Stir continuously until the mixture is completely smooth and glossy.

Carefully remove the bowl from the heat and thoroughly whisk in both the granulated and dark brown sugars. The ambient heat will help dissolve the sugars.

Add the eggs to the warm chocolate mixture all at once. Now, using a strong balloon whisk, beat the batter aggressively and continuously for exactly one full minute. Do not cheat the time. This specific aeration is what creates the coveted, shiny, crackling crust on the finished brownies.

Remove the whisk. Using a rubber spatula, gently fold the cocoa powder, crema pastry flour, and kosher salt into the aerated batter just until the dry streaks disappear. Do not overmix.

Pour the thick batter into the prepared pan, smoothing the top. Bake for exactly 25 minutes. A tester inserted into the center should emerge with sticky, fudgy crumbs, not wet batter.

Let the brownies cool entirely in the pan. Using the parchment paper overhang, lift the block of brownies onto a cutting board and slice into 16 perfect squares. Serve with cold milk or melted over vanilla ice cream.