Preheat oven to 350F. Line an 8x8-inch metal baking pan with parchment paper, leaving a 2-inch overhang on two sides for easy lifting. Lightly grease any exposed pan surface.

In a medium saucepan over low heat, melt butter and semisweet chocolate together, stirring frequently until smooth and glossy, about 4-5 minutes. Remove from heat immediately to avoid scorching.

Whisk granulated sugar and brown sugar into the warm chocolate mixture until fully combined. The mixture will look thick and grainy at first but will smooth out. Let cool 5 minutes so the eggs don't scramble.

Whisk in eggs one at a time, beating well after each addition until the batter looks shiny and pulls away from the sides of the pan. Whisk in vanilla.

Using a rubber spatula, fold in flour, cocoa powder, and salt until just combined and no dry streaks remain. Do not overmix - this keeps the brownies fudgy.

Fold in 3/4 cup white chocolate chips. Reserve the remaining 1/4 cup for topping. The batter will be thick and glossy.

Spread batter evenly in prepared pan. Sprinkle remaining 1/4 cup white chocolate chips on top, pressing gently to adhere. Bake 26-30 minutes until the top is crackly and a toothpick inserted in the center comes out with moist crumbs but no wet batter. The edges will be set but the center should still jiggle slightly.

Let cool in pan on a wire rack for at least 45 minutes. Use parchment overhang to lift out, then cut into 16 squares. For cleanest cuts, chill 30 minutes first.