Cream 3/4 cup butter and white sugar together in mixing bowl.
Stir in eggs, blending well, then add sour cream and vanilla extract.
Separately in small bowl, stir together flour, baking powder and salt.
Add flour mixture to wet ingredients until just combined.
Stir in apples.
Place half batter in prepared pan.
Sprinkle with cinnamon filling.
Pour remaining batter on top.
Sprinkle cinnamon streusel topping on top.
Bake for 60 - 75 minutes or until cake tester comes out clean. (Your cake may need even longer depending on the moisture content of the apples.)
Loosen all accessible edges with sharp knife.
Carefully lift out of cake pan and place on cake platter.
(I used two hard metal spatulas underneath the bottom of the cake to lift it out of the the pan. )