Line a 12-section bun tray with paper cake cases.
Put the sugared rose petals and caster sugar in a food processor and process until the rose petals are chopped into small pieces. Tip into a bowl and add all the remaining cake ingredients. Beat with a hand-held electric whisk for about a minute until light and creamy. Divide the cake mixture between the cake cases.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 20 minutes or until risen and just firm to the touch. Transfer to a wire rack to cool.
Beat together the mascarpone, icing sugar, lemon juice and food colouring, if using, with a wooden spoon in a bowl until smooth. Spread over the tops of the cakes using a small palette knife and decorate with extra sugared rose petals.