Melt the butter in a small saucepan over medium-low heat. Once it melts reduce the heat to low and cook for 2-3 minutes, swirling the pan frequently until you smell something nutty and the milk solids turn golden brown. Set aside to cool.
Whisk the all-purpose flour, pastry flour, cornstarch, baking soda, and baking powder in a large mixing bowl until combined.
Whisk the salt, sugar, buttermilk and eggs in a medium mixing bowl until salt and sugar have dissolved and the mixture is smooth.
Drizzle the browned butter into the flour mixture and work it in with a silicone spatula at first, then switching to your fingers to evenly coat all the flour with the butter, a lot like making biscuits or pie dough.
Pour the buttermilk mixture into the flour and whisk just enough to combine without over mixing. It will be lumpy this time, but that's ok. Rest for 5 minutes...the batter, not you.
Meanwhile, heat your waffle iron to the manufacturer's instructions on the medium-high setting.
Ladle or scoop about 4 ounces (1/2 cup) of batter onto the grates of the iron. Close the lid and cook until golden brown, about 3 minutes. (Again, if you don't trust the waffle iron's surface, hit it lightly with nonstick cooking spray.)
Serve immediately or hold briefly on a cooling rack set in a 200 ℉ oven until ready to serve. Do not stack, unless you like the sound of "soggy waffle."