Line a baking sheet with greaseproof paper. In a spotlessly clean bowl, whisk the egg whites with a hand-held electric whisk until stiff.
Tip the sugar onto a plate. Carefully pull the rose petals off the flower heads. Brush a rose petal with a little egg white, then dip into the sugar. Shake off any excess and place on the greaseproof paper to dry. Repeat with the remaining rose petals.
For best results, leave for 1–2 hours until completely dry. Peel off the paper, then use to decorate puddings, cakes and milk drinks.