Pare and core apples, slice thin. Simmer in cider 5 mins, or until just tender. Drain, reserving cider.
Combine 2 T cider, brown sugar, walnuts and butter on the bottom of a 13x9 pan. Set in 350-degree oven for 5 mins; then remove from oven.
Prepare cake mix, using rest of reserved cider plus any additional water needed for water portion for cake mix.
Arrange apple slices over brown sugar mixture in pan. Pour batter over apples, and bake at 350 degrees for 40 mins, or until done. Invert, and let stand one minute, remove pan.