Preheat oven to 350 degree F. Line a 9 x 13 baking pan with aluminum foil.
Using a small saucepan, melt butter over medium heat until it melts. Remove from heat.
In a bowl, whisk together flour, salt and baking powder.
Using an electric mixer, mix together brown sugar and butter. Add in 2 teaspoons vanilla and 3 eggs. Mix until combined. Mix in the flour mixture until just combined.
In a separate bowl, beat together softened cream cheese, sugar, 1/2 teaspoon vanilla and 1 egg.
Spread blondie mixture into baking dish. Spoon dollops of cream cheese mixture dots over top of blondie mixture.
Swirl the cream cheese mixture either with toothpick or knife for a marbling effect.
Bake for approximately 25-30 minutes.
Place pan on wire rack and let cool completely before serving.