Preheat the oven to 180°C/gas mark 4. Beat the butter and sugar together for two minutes, until light and fluffy. Beat in the egg and vanilla extract. Stir the flour and salt into the egg mixture to form a dough.
Mix the chocolate and rose petals through, cover and chill for at least 2 hours or up to 3 days to firm up. The flavours will deepen over time.
Line a large baking sheet with baking paper and use an ice cream scoop (or a soup spoon) to form balls of cookie dough. Space the scoops out well – 6 in a batch is plenty as they will spread – and bake for about 15 minutes, until pale golden. Leave to firm up on the tray for a few minutes, then transfer to wire racks while you cook the next batch. Store in an airtight container.