Preheat the oven to 325 degrees F (165 degrees C). Lightly grease a 9x9 inch metal baking pan and line it with parchment. Set aside.
Melt the butter and the white chocolate together in a double boiler over medium-low heat. Stir continuously to ensure the white chocolate gets heated evenly. Then remove from the heat.
8 oz (226 g) white chocolate bars, chopped (Lindt, Ghirardelli or something similar), 3/4 cup (168 g) unsalted butter, chopped into small cubes
Add the eggs, egg yolks, sugar, lemon zest and vanilla to a large bowl and whisk together until pale and smooth. (You can also use an electric hand mixer on high speed to make it easier.)
2 eggs, 2 egg yolks, 1 1/4 cups (250 g) granulated white sugar, 1/2 tbsp vanilla extract, 3 tbsp (15 g) lemon zest (3-4 lemons zested)
Pour in the white chocolate and melted butter mixture and whisk until combined and smooth.
Fold the flour and salt into the wet ingredients with a rubber spatula just until combined.
1 3/4 cups (219 g) all-purpose flour, spooned and leveled, 3/4 tsp salt
Pour the lemon brownie batter into the prepared pan. Use a mini offset spatula to smooth the batter out.
Bake the brownies for 32-36 minutes. (Cover the pan loosely with parchment paper towards end of baking if the brownies are getting too brown.)Then let the brownies cool completely in the pan on a wire rack. Once cool, use a butter knife to loosen the edges of the brownies from the pan, and pull up on the parchment paper to gently release.