In a small bowl, add flour and salt and whisk together. Set aside.
Line an 8x8 baking sheet with parchment, set aside. Preheat oven to 350°F
In a double boiler, or a bowl over a small sauce pan of simmering water, add your chopped white chocolate, butter and oil. Stir occasionally until melted. Remove bowl from heat and allow to cool.
In a large bowl or the bowl of your stand mixer, add granulated sugar and eggs plus additional yolk. Mix on medium for 4-5 minutes. Eggs will be slightly foamy and voluminous.
Slow your mixing to low and slowly pour in your melted white chocolate, butter, and oil mix. Mix until combined.
Add in your dry ingredients and mix until flour is JUST combined. Do not overmix.
Pour in your white chocolate chips and stir into the batter.
Pour your batter into your prepared pan and smooth out into an even layer.
Place into your oven on the center rack and bake for 25-30 minutes. The center should be set. Allow to completely cool before cutting into and enjoying. Store in an airtight container.
