Heat oven to 350° F.
Mix streusel until crumbly.
Beat remaining ingredients in large mixing bowl for about 2 minutes, scraping bowl
Spread half of batter in a greased 9×9 pan.
Sprinkle with half of streusel mix.
Repeat layers with remaining batter and streusel.
Bake until wooden toothpick inserted into center comes out clean, about 35-40 minutes.
In heated oven, melt butter in pan.
Sprinkle with brown sugar.
Arrange apples in pan.
Pour all of batter in pan and top with streusel and bake as above.