Special equipment: a candy thermometer
Combine the maple syrup, brown sugar, cream, condensed milk, corn syrup and salt in a saucepan. Stir over medium heat until the mixture reaches 245 degrees F on a candy thermometer. Take from the heat and stir in the butter. Pour into a 6-inch square baking pan lined with parchment and allow to cool and set about 3 hours.
Take the caramel from the pan and, using a very sharp knife gently sprayed with nonstick cooking spray, cut the caramels into squares and wrap in wax paper or candy wrappers (see Cook's Note). Store in a cool dry place.
If the caramel feels too soft when cutting, put it into the freezer for 30 minutes, then finish cutting.