Whisk flour with sugar, baking powder and salt in a small bowl.
Whisk milk with oil, eggs and vanilla in a large bowl.
Whisk in flour mixture until combined.
Stir in 10 chopped caramel butter cookies.
Scrape mixture into a well-oiled 10-inch cast-iron skillet, smoothing top.
Set the pan over a grill on medium, lid closed, or on a campfire grill, covered, until a tester inserted into the centre of the cake comes out clean, 30 to 40 minutes.
Immediately sprinkle with marshmallows.
Let stand to cool slightly, then top with the remaining 6 chopped cookies and strawberries.
Tip
Shortcake can be baked in the centre of a 350F oven, 40 min. Camping? For easy travelling and cleanup, whisk then store dry ingredients and prepared shortcake toppings in reseal-able bags.