Lightly grease the leaf mould
Put the maple syrup in a big pan, it will bubble heavily and could exit the pan.Turn on the fire until it bubble, add butter and mix very well. Control with a thermometer the temperature, it should be very close to 115°C/240°F.At that point remove from heat and mix vigorously until the caramel turns opaque and looses the shine. Quickly pour it into the moulds and let the candies harden.
The tricky part of this recipe is understanding when it's time to pour the caramel: if too little mixing the candies will not harden, too much mixing and it will harden too fast.In this case just put the caramel on fire again and restart the procedure. You can keep the candies stored into a metal box.