Line your baking sheet with parchment paper (or your favorite silicone mat).
In a medium bowl, mix together the spice cake mix, oil, eggs, ground ginger, cinnamon, and vanilla until a soft dough forms. It will be thick and sticky, that’s exactly right for a gingerbread cake mix cookie.
Use a cookie scoop for even portions. Roll them gently and flatten slightly with your hand.
Bake for 9–11 minutes, just until the tops are set. They stay soft as they cool, so don’t overbake.
Cool completely.
Frosting:
Beat the butter in a medium bowl until smooth.
Add the powdered sugar, milk, cinnamon, and vanilla.
Mix until light and creamy. Add more milk if you want it smoother.
Frost your cooled cookies, then add sprinkles, sanding sugar, or festive edible decorations.