Preheat oven to 350 degrees. Line an 8×8 or 9×9 pan with parchment paper (use a little butter to help it stick).

In a medium bowl, whisk the flour, malted milk powder, and salt; set aside.

Cut the unsalted butter into chunks and heat in a small saucepan pan over medium heat. When the butter begins to foam, then subside, watch carefully; as soon as the solids begin to brown and fragrant, remove pan from heat. 

In the bowl of a stand mixer, combine the hot brown butter with the sugars and beat until well-mixed, 2-3 minutes. Scrape down the sides and bottom of the bowl. Add the vanilla and both eggs and beat until the mixture is light and fluffy, another 2-3 minutes. On the lowest speed, add the flour mixture until all traces of flour are incorporated. Beat another 30 seconds or so. The batter will be very thick, almost like cookie dough; do not be alarmed. 

Scrape the batter into the parchment-lined pan and spread evenly. Bake at 350 for 20-25 minutes, until a toothpick or cake tester come out clean. While the blondies are still warm, garnish with flaky sea salt, if desired.

Allow to cool in the pan, then flip or lift the blondies out onto a cutting surface and cut into squares.