1. Put the butter, sugar, lemon zest, rose water (to taste) and vanilla in a large bowl and, using an electric mixer, beat together for about 5 minutes or until light and fluffy. Scrape the bowl down and add the flour, a pinch of salt and the rose petals, mixing together briefly until it comes together as a dough. Tip the dough onto the work surface and bring together into a ball. Flatten with your hands, then roll out to a 25cm square; place on a baking tray and chill until firm – about 30 minutes.
2. Preheat the oven to 170˚C, gas mark 3; line 2 baking trays with parchment. Halve the dough, then cut into 2.5cm-thick fingers and pierce all over with a fork.
3. Put the biscuits on the prepared baking trays and bake for 25-30 minutes or until lightly browned. Remove from the oven and allow to cool completely.
4. Put the chocolate in a heatproof bowl and microwave in 30 second bursts until about ¾ of the chocolate has melted. Mix vigorously with a spatula until fully melted (this is a quick method of tempering the chocolate). Dip the shortbread halfway into the chocolate, allow the excess to drip off, then lay on a clean sheet of parchment to set, decorating with a few extra rose petals. Once the chocolate has set, you can store the shortbread in an airtight container for up to 4 days.
Photograph by Tara Fisher, recipe and image courtesy of Waitrose & Partners Food, created by Edd Kimber