Preheat oven to 350 degrees.
Peel and slice apples - 8 slices per apple.
Melt butter in microwave (1 - 1 ½ minutes).
Mix sugar, cinnamon, and vanilla.
Roll one apple slice into crescent roll.
Place in 9x13 pan and pour cinnamon mixture over apples that are in crescent rolls.
Pour Mountain Dew around apple dumplings.
Cook in oven at 350 degrees for 30-40 minutes.