In a bowl, cream butter and sugar. Beat in eggs and vanilla. Combine flour, baking powder and salt; add to creamed mixture alternately with milk. Stir in cranberries. Pour into a greased 13-in. x 9-in. baking pan. Sprinkle with marshmallows. Lightly press into batter. Sprinkle with brown sugar and pecans. Drizzle with butter. Bake at 350° for 35-40 minutes or until cake tests done.