Heat oven to 350 degrees. Butter and flour 13x9-inch baking pan.
Place ice cream in refrigerator and let soften 20 minutes.
Meanwhile, prepare cake: using electric mixer, beat butter in large bowl until creamy. Gradually beat in sugar and continue to beat until very light and fluffy. Sift cake flour, baking powder, baking soda, and salt onto sheet of waxed paper. Beat eggs into butter mixture one at a time. Beat in vanilla. Reduce speed on mixer and mix dry ingredients and buttermilk alternately into batter, beginning and ending with dry ingredients. Do n ot overmix or cake will be tough. Pour batter into prepared pan and spread evenly. Scatter apples evenly over top.
Make topping: process flour, walnuts, sugars, cinnamon and butter in food processor until butter pieces are size of small peas. Add coconut and process until just combined. Sprinkle cake until toothpick inserted in center comes out clean, about 45 minutes.
While cake is baking, scoop 1 pint ice cream into mixing bowl, sprinkle with half the 1-1/2 t. cinnamon, and fold lightly together with rubber spatula. Return ice cream to container. Repeat with remaining ice cream and cinnmon. Freeze until ready to serve.