Preheat oven to 350 °F / 180 °C and line two trays with parchment.
Make the caramel: combine condensed milk, brown sugar, butter, and salt flakes in a small saucepan. Stir over medium heat for 4–5 minutes, until golden and thickened. Cool 5–10 minutes until thick but pourable.
In a large bowl, beat margarine, brown sugar, and salt until creamy.
Add oil, maple syrup, and vanilla; mix until smooth.
Stir in ginger, cinnamon, nutmeg, and cloves.
Sift in flour and baking soda. Stir until a soft dough forms. If dough is not sticky enough to shape, add a tiny splash of milk (about 1/2 tbsp) until it can be rolled into balls.
Roll tablespoon portions into balls and arrange on lined trays about 5 cm apart.
Press your thumb or the back of a teaspoon into each ball to make an indent. Add a dollop of caramel (about a 1/2 tablespoon) onto each cookie.
Bake 9–10 minutes, until edges are set and centers are still soft. Caramel will remain gooey.
While warm, top each cookie with a few Cornish sea salt flakes.
Cool 10 minutes before moving to a rack.