Preheat oven to 350°. Line a 13x9-in. baking pan with parchment, letting ends extend 1 inch over the sides., In a large bowl, cream butter and brown sugar until light and fluffy, 5-7 minutes. Beat in eggs and vanilla. In another bowl, whisk flour, baking powder and salt; gradually beat into creamed mixture. Spread onto bottom of prepared pan., In a small bowl, mix sugar and cinnamon; sprinkle 2 tablespoons mixture over batter. Bake until edges are light brown, 25-30 minutes. Cool completely in pan on a wire rack., Spread dulce de leche over crust. In a small saucepan, combine white baking chocolate, cream and corn syrup; cook and stir over low heat until smooth. Cool slightly. Spread over dulce de leche. Sprinkle with remaining cinnamon sugar. Refrigerate, covered, at least 1 hour., Lifting with parchment, remove from pan. Cut into bars. Refrigerate leftovers.