Preheat the oven to 350F (180 C).

Prep the Pan

1. Lightly spray an 8″x8″ pan with cooking spray.
2. Cut a piece of parchment

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    to line the bottom and sides of one side. Spray over the top of this piece of parchment

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   , then cut another one to go across the remaining 2 sides of the pan.

Brown the Butter

1. Melt the butter over low heat in a small pan until the foam starts to subside and there are brown flecks in the bottom of the pan. On low heat, this will take about 10 minutes.

Dissolve the Sugar

1. While the butter is browning, fill the bottom of a double boiler

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   with about 1″ of water, then bring it to a boil.
2. Use a whisk to mix the sugars, baking powder, salt, whole egg and the egg yolk in the top of a double boiler

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   .
3. Lower the water to simmer, then set the top pot over the water, stirring constantly for about 4 minutes. In this time, the mixture will get thinner, paler, and all of the sugar will dissolve.
4. Once the butter has browned, set it in a bowl to cool slightly.
5. Whisk the egg/sugar mix into the butter. If it splits, keep whisking. As it cools, it will come back together. Add in the vanilla.
6. Allow the butter mix to cool until it’s thick and no longer warm to the touch. It will be noticeably thicker and glossy.

Add the Flour and Mix-Ins

1. Fold in the flour, 4 tablespoons of the sprinkles, and all but a few of the white chocolate chips with a baking spatula

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   until the flour disappears.
2. Smooth the batter into the prepared pan.  

Finish the Blondies

1. Sprinkle the remaining tablespoon of sprinkles and the rest of the white chocolate chips on top of the batter.
2. Bake for 16-18 minutes until the edges are browning and the middle is no longer jiggling.
3. Cool the bars completely before cutting into 9 large bars or 16 smaller bars.