Preheat oven to 325° and grease 9-inch square pan. In small saucepan, melt chocolate and butter or margarine over very low heat, stirring constantly. Cool. In small bowl, beat cream cheese and 1/4 cup sugar until light and fluffy. Beat in 1 egg, 1 tablespoon flour, lemon juice and 1/2 teaspoon vanilla. Spread in pan. In another bowl, beat remaining 2 eggs until fluffy and light in color. Gradually add remaining 3/4 cup sugar, beating until thick. Fold in remaining flour, baking powder and salt. With a knife or spatula, swirl mixture just until marbled. Bake 30 to 35 minutes, or until toothpick comes out clean. Cool; cut into bars. Cover and store in refrigerator. Makes 32 brownies.