Preheat oven to 350°F. Line a 9x9 square baking pan with parchment paper, leaving an overhang for easy removal of the blondies. Spray lined pan with baking spray.
Melt butter in a light-colored saute pan, stirring frequently, until milk solids separate and begin to turn a deep golden brown. You should smell a nutty aroma. Remove from heat immediately and pour the butter into a large heatsafe mixing bowl, scraping all the brown bits along with it.
Add half of chopped white chocolate (about ⅓ cup) to the browned butter and stir to melt chocolate until mixture is smooth.
Whisk in brown sugar until smooth.
Whisk in eggs, one at a time, followed by vanilla, mixing after each addition.
Stir in almond flour and mix well. Mixture will be thick.
Fold in remaining chopped white chocolate and roasted macadamia nuts, if using.
Bake in preheated oven for 25-30 minutes, or until the top of the blondies are lightly browned and a toothpick entered into the center of the pan comes out clean. Cool before slicing.
Almond Flour: For this recipe, I recommend Bob's Red Mill Super-Fine Almond Flour. There is a real difference in the texture and result achieved depending on the brand and type of almond flour you use, and Bob's Red Mill almond flour has always given me great results!How to Roast your Macadamia Nuts: If you can't find roasted macadamia nuts in the supermarket, pick up some raw ones and just toss them on a lined baking sheet. Bake them in a 325-degree oven for about 10 minutes, or until they're lightly browned. Let them cool before adding them to your blondies, and try to resist eating them all before you can use them to bake! They're SO good!