My sister asked me what the difference was between blondies and the chocolate chip cookies I usually make. The answer is the butter. In blondies, the butter is melted and you essentially make a flowing batter to pour into a cake tin. With cookies, the butter is room temperature but still solid and it gets whipped and creamed together with sugar and the batter is much more solid and doughy.

Taste-wise, the two are kindred spirits considering the ingredients are quite similar. Texture-wise, blondies are more gooey and a bit more decadent because it's a bit chunkier and denser. I also really love blondies because they do not require the aid of an electric mixer, the butter doesn't have to be sat out on the counter ahead of time, and the batter whips together in the time it takes the oven to preheat.
Ingredients [9" x 9" pan]
½ cup melted butter
1 cup loosely packed brown sugar
1 tablespoon molasses
1 egg
1 teaspoon vanilla extract
1⅓ cups flour
1 teaspoon baking powder
1 teaspoon coarse salt
4 oz. chocolate, chopped

There's no real right or wrong way to start, but I like to grab the butter, pop it into a saucepan, and get it melting over low heat right away. While that's going, I will whisk together the dry ingredients and chop up the chocolate.
I decided to mix in a bit of white chocolate and 60% cacao chips. You could also mix in whatever else you like, toffee bits, butterscotch chips, marshmallows, pretzel bits, sprinkles, etc.

Add brown sugar and molasses to the melted butter and whisk together.

Crack in an egg and whisk in some vanilla extract.
Slowly whisk in the dry ingredients until a thick batter forms.
Use a rubber spatula to fold in the chocolate and then spread the batter into a pan. I also gave the top a sprinkle of coarse Himalayan salt, which I also recommend you do.
Bake at 350F for about 20 minutes, or until the blondies are set and the batter isn't jiggly. I prefer mine slightly underdone so I start checking on them around 18 minutes.
Let these cool briefly before serving. Ideally, they'll be served still warm from the oven because that's when they're best.
These are chewy and decadent and sweet, but that little bit of salt on top gives it balance. I also love the bitterness of the 60% cacao chips, but if you've got a stronger sweet tooth, use semisweet or milk chocolate for extra sugar. And like I said, because I prefer them a little underdone, I really enjoy the gooey texture of the center contrasted with the crisp top and edges.
I also made a batch of ultra loaded blondies to take to our last clay class. They were a hit.
Here's the recipe page: