In a large bowl, combine cake mix, oats, nutmeg, and butter at low speed until crumbly.
(If mixture is still too moist to crumble, add two level tablespoons oats, one tablespoon flour, and mix to crumbly).
Reserve one cup crumbs for topping.
To remaining crumbs in bowl, add one egg, blend in egg until well mixed.
Press mixture into bottom of prepared baking pan.