Rub some butter around the inside of an 18 x 23cm/7 x 9” baking tray or insert a baking liner.

Measure the supergrain hoops into a bowl.

Put the butter into a mixing bowl and microwave on full power for 10 seconds.

Add the marshmallows and microwave on full power for 50 seconds.

Remove the bowl, add the supergrain hoops and mix well.

Immediately tip the mixture into the baking tray, pushing it into the edges and flattening the top. Chill until set.

Cut into slices and store an airtight tin for up to a week.