Preheat the oven to 325 F. Line a 9 x 13-inch baking dish with parchment paper and coat with cooking spray or grease with butter.
In a heatproof bowl, microwave the chocolate chips and butter in 30 second intervals, stirring after each time, for about 1.5-2 minutes total, until just melted. You could also do this in a double boiler set over simmering water.
Using a handheld whisk or stand mixer, whisk both sugars into the melted chocolate. Add the eggs, one by one, until combined, then the vanilla and salt. Whisk to combine.
Add all the flour at once and gently mix until just combined.
Pour the brownie batter into the prepared pan and bake for 27-33 minutes in a convection oven or 32-36 minutes in a standard oven. The brownies are done when a toothpick inserted 2 inches from the edge of the pan comes out clean. The center should still look slightly underbaked, with perhaps a single crack or two showing along the top.
Allow the brownies to cool completely in the pan.