Preheat the oven to 350 ºF (175 °C). Butter an 8x8-inch metal brownie pan and line the bottom with a square of parchment. Set aside.
In a medium bowl, whisk together the flour, salt, baking powder, and baking soda. Set aside.
In a small saucepan on medium–high heat, melt the butter, swirling the pan often. Continue heating the butter and swirling often until the milk solids at the bottom of the pan begin to brown. The browned butter will smell nutty when it's done. Set aside to cool slightly.
In a large bowl, using an electric hand mixer, whip together the browned butter, the granulated sugar, and the brown sugar until it's well mixed.
Add the egg and the vanilla, and mix well until the mixture is light and fluffy. Make sure to clean down the sides of the bowl as needed with a big spatula.
Dump in the whisked dry ingredients, and incorporate them either with the hand mixer on low, or by hand with a big wooden spoon.
Mix in the chocolate. The dough should be quite thick.
Transfer the dough to the prepared pan and pat it out from edge-to-edge so that it fills the pan completely.
Scatter the raspberries over the dough.
Bake the blondies for 30 to 40 minutes. Less for a more gooey blondie, longer for a chewy blondie. I like to bake blondies until the edges are nicely browned.
Let the blondies cool completely before cutting into squares (9 large squares or 16 smaller squares).