Line a 13 x 9-inch pan (metric is approximately 3L) with foil and spray with non-stick spray.

Melt butter in a heavy saucepan over medium heat. Add the evaporated milk and the sugar.

Bring to a boil, stirring constantly and boil for 4-5 minutes. It's strongly suggested that you use a candy thermometer to see if the mixture is 235 F/113 C which is the temp for "soft-ball" stage. You can also test this by using the cold water method (see post).

Once the mixture is at soft-ball stage, add the entire 7 oz jar of fluff and the white chocolate chips. Stir until the morsels are melted and everything is well incorporated.

Spread it in the prepared pan and chill for at least 2 hours. Cut into squares of the desired size (up to you).