Preheat the oven to 350°F.

Butter or coat with cooking spray a 9 X 9 inch square baking pan.

For the Pistachio paste.

Bring a small pan of water to boil. Add the 1 ½ cup of pistachios and let boil for 1 full minute.

Drain the pistachios and let cool briefly on paper towels to get any excess moisture off the nuts.

Using your fingers and the paper towels, rub off the outer skins of the pistachios. It may take a bit of effort, but it is worth it. You don’t have to be perfect, its more for the color.

In a food processor or blender, process the remaining pistachios until very finely ground. Add the powdered sugar and the water and process until very smooth, and it makes a paste. This will take about 5 minutes.

Add the 1 teaspoon vanilla and process until well blended. You should end up with a little more than ½ cup pistachio paste.

To make the batter.

Combine the flour, salt, and baking powder in a bowl or 4 cup measuring cup and set aside.

In a large mixing bowl, beat together the butter, brown and white sugars. Beat until well creamed and fluffy, about 3 minutes.

Add the eggs, egg yolk, and 1 tablespoon vanilla, beat until well blended in, and the mixture is again fluffy for about a minute.

Stir in by hand the flour mixture.

Spread the batter into the 9 X 9 inch prepared pan.

Drop the pistachio paste on top of the batter in large spoonfuls and use a butter knife or even your clean fingers to make big swirls. Do not over-swirl–you want big ribbons of Pistachio Paste.

Bake for 30 to 40 minutes or until the brownies are golden brown and set on the edges and the center has puffed up. The middle will still be pretty doughy, but they will continue to cook as they cool!

Once the pistachio blondies are cool, cut into squares.