Using a mixer fitted with the whisk attachment, whisk eggs and sugar on high speed until thick and pale, 4-5 minutes. Turn off mixer. Slowly add in chocolate mixture and fold, using a rubber spatula, until combined. Add flour mixture and keep folding just until combined. Fold in white chocolate.
Pour batter into prepared pan and smooth the top. Bake for 15-18 minutes. Don’t open the oven door in the first 13 minutes of baking. Mine are ready in 15 minutes, it sounds too short but these brownies aren’t very thick and it’s important to keep them fudgy, so be careful not to overbake. A toothpick inserted into the center of the brownies should come out moist, not dry. Let brownies cool completely on a wire rack. You can refrigerate until set for easy cutting. Lift brownies out of the pan using parchment paper and cut into bars. Slightly warm they’re heavenly!