Preheat the oven to 350°F and line an 8×8 square baking pan with parchment paper. Leave parchment paper hanging over the sides of the pan so that you can easily remove the blondies from the pan later.
Melt the butter in the microwave or in a small pan over the stove. Transfer the melted butter to a medium sized bowl.
Add in both the sugars and use a whisk to whisk the butter and sugars together. Keep whisking until the mixture resembles a paste that pulls away cleanly from the side of the bowl when you mix it.
Add the eggs and vanilla and mix again. Pour the flour and salt into the bowl and mix with the whisk until just combined (it should only take about a minute). This is important, because over-mixing at this stage will affect the texture of the blondies!
Gently fold in the chopped chocolate until just combined. Pour the batter into the lined baking pan using a spatula to scrape all the batter out of the bowl.
Bake for 25-35 minutes. The top of the blondies should be crinkly and when you insert a toothpick in the middle the toothpick should not come out clean. The blondies are ready when the toothpick has a few wet crumbs, but not wet batter.
Let the blondies cool completely before slicing. Enjoy!