Preheat oven to 350 degrees. Line an 8x8 inch glass baking pan with two sheets of aluminum foil, one going in one direction and the other in the other direction like a cross. Butter the foil with the 1 tablespoon of butter. Set aside.

In a large mixing bowl, beat the butter, brown sugar, granulated sugar and confectioner’s sugar until the mixture is light and fluffy, about 2 minutes. Add vanilla and salt and beat until just combined. Add the flour all at once and beat at low speed for a minute until the flour becomes crumbly like a crumb topping.

Remove 1½ cups of the butter mixture to a small bowl and refrigerate until the blondie batter is ready.

To the remaining mixture in the large bowl, add the egg and baking powder and beat the mixture for a minute until the mixture is no longer crumbly. Fold in 1 1/4 cups of white chocolate chips.

Carefully spread the blondie batter into the baking pan making sure to keep the foil flat against the sides and bottom of the pan. The batter will be thick.

Bake the blondie mixture for 20 minutes and remove from the oven.

Crumble the topping all over the top of the blondies and then sprinkle them with ½ cup of white chocolate chips. Bake the blondies with the crumb topping for 30 minutes. Check to see if the top is a light golden brown as the white chocolate chips should be just lightly roasted.

Remove pan from the oven and let cool for at least an hour before cutting into squares.

You can serve these with a glass of milk or top with vanilla ice cream and hot fudge sauce.