Preheat the oven to 350 ºF (175 °C). Butter an 8x8-inch (20x20-cm) 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 chopped Easter 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. You can use a flat-bottomed glass to press the dough into the corners and smooth it out.
Bake the blondies for 25 to 30 minutes. Less for a more gooey blondie, longer for a chewy blondie. I like to bake blondies until the edges are nicely browned and chewy.
Let the blondies cool completely before cutting into squares (9 large squares or 16 smaller squares).
Store in an airtight container.
Notes
For softer, more gooey blondies, use less flour, as little as 125 grams (1 cup)For a 9x9 brownie pan, the blondies will be thinner and will take less time to bake. Start checking them after 20 minutes to see if they are done!You can also bake this recipe in a 7x11-inch rectangular metal baking pan.