Preheat oven to 325 degrees. Line a 13x9x2 -inch baking pan with foil, extending over the edge of pan. Lightly spray with nonstick baking spray.
In a small bowl, combine cream cheese and the 2 tablespoons of butter. Beat with an electric mixer on medium-high speed until mixture is fluffy.Gradually add the ¼ cup sugar, beating until light. Beat in the 1 egg and the 1 tablespoon flour just until combined. Set aside
In a small bowl, combine the 1-¼ cups flour, the baking powder, and salt. Set aside.
In a medium saucepan, combine chocolate and the ¾ cup butter. Cook and stir over low heat just until melted. Transfer to a large bowl. Gradually add the 2-¼ cups sugar, beating on low speed until combined. Add the 4 eggs one at a time, beating after each addition. Beat in milk and vanilla. Gradually beat in flour mixture.
Spread the chocolate batter in the prepared baking pan. Spoon cream cheese mixture in mounds on top of chocolate batter. Using a table knife or narrow metal spatula, gently swirl the cream cheese mixture into the chocolate batter to marble.
Bake for 40 to 45 minutes or until a toothpick inserted in the center comes out with moist crumbs attached. Cool in pan on a wire rack. Use the foil to lift uncut brownies out of pan. Cut into brownies. Store, tightly covered, in the refrigerator for up to 3 days. Makes 42 servings.