Preheat oven to 350° F. Prepare an 8x8-inch baking pan by lining with parchment paper and spraying bottom and sides lightly with cooking spray.
In a medium sized bowl, combine the butter, brown sugar, egg, egg yolk and vanilla. Stir with a whisk until fully combined.
8 tablespoons unsalted butter, melted, ¾ cup brown sugar, packed, 1 egg, 1 egg yolk, 2 teaspoons vanilla
Add the flour, salt and baking powder. Using a rubber spatula, fold flour mixture into butter mixture just until combined.
1 cup flour, 1 teaspoon salt, ½ teaspoon baking powder
Fold in chopped white chocolate.
1 cup chopped white chocolate or white chocolate chips
Pour batter into a prepared baking pan. Using an offset spatula, spread batter to the edges in an even layer.
Drop the raspberry sauce in tablespoonfuls all over the top of the batter. Using a knife, drag it through the batter and raspberry sauce to create swirls in the top, making sure to go all the way to the edges.
Bake in 350°F oven for 25-27 minutes or until the edges just begin to brown. Remove from oven and let cool completely before removing from pan and cutting into squares.