Lightly brush the sides and base of a 6” square cake tin with oil.
Line with non-stick baking paper; lightly brush baking paper with oil.
Place cream, sugar, butter, and corn syrup into a medium-sized heavy-based deep saucepan.
Stir over a high heat until sugar dissolves.
Reduce heat to low and cook stirring occasionally until caramel reaches 240°F on a candy thermometer, about 25 minutes (or until a small amount of caramel dropped into chilled water forms a soft, flexible ball, but flattens like a pancake after a few moments in your hand). It is important not to overcook the caramel or it will result in a hard caramel and not a chewy caramel).
Remove from heat and pour into prepared tin.
Allow to cool at room temperature, about 4 hours.
Remove caramel from tin and cut into small cubes, about 1⁄2” each.
Line a 11″ x 7″ tin or with aluminum foil.
Place marshmallows, peanuts, and caramel into a large mixing bowl.
Melt dark chocolate in a heatproof bowl over a saucepan of simmering water.
Allow chocolate to stand 6 minutes to cool but not set.
Pour chocolate into marshmallow, caramel, and peanut mix and gently mix until just combined.
Spoon into prepared tin.
Refrigerate until firm, about 2 hours.
Remove from tin and cut into snack size pieces using a warm sharp knife.
To maintain an optimum texture, store in a cool dark place, not in refrigerator.