Line the bottom and sides of a 9-by-5-inch loaf pan with parchment paper; brush the parchment with vegetable oil. Bring the maple syrup to a boil in a large saucepan over medium heat, then reduce the heat to medium low. Dip the back of a spoon in vegetable oil and run it over the top of the foam to help it subside. Increase the heat to medium and continue cooking until a candy thermometer registers 246 degrees F, 25 to 30 minutes. Pour the syrup into a heatproof bowl and let cool, 5 minutes.
Beat the syrup with a mixer on medium-low speed until it starts to lighten in color and turn opaque, 30 seconds to 1 minute. Pour into the prepared pan and spread with an offset spatula; let cool completely, about 1 hour. Lift out of the pan and cut into pieces.