Preheat oven
Preheat oven to 350°F (175°C). Line an 8×8-inch pan with parchment paper.
Melt chocolate & butter
Gently melt white chocolate and butter together over low heat or using a double boiler. Stir until smooth and let cool slightly.
Mix wet ingredients
Whisk sugar into the melted mixture, then add eggs one at a time. Stir in vanilla.
Add dry ingredients
Fold in flour and salt just until combined. Do not overmix.
Bake
Pour batter into prepared pan and smooth the top. Bake for 22–26 minutes, until edges are set and the center is just slightly soft.
Cool & slice
Let brownies cool completely before slicing.