Make the strawberry rose syrup. Put all the ingredients into a saucepan and cook over medium-low heat, stirring, until the strawberries start to release their juice about 5-10 minutes. Strain into a bowl, pressing on the strawberries. Cool before using.
Preheat the oven to 180C (350F). Spray 2 x18cm/7in cake tins (or 2x23cm/9in tins) with cake release and line with baking parchment. Spray the parchment too.
Put the flour, sugar, baking powder and salt in the bowl of your stand mixer fitted with a paddle attachment and briefly mix together on low speed to combine.
Add the cubed butter and mix on low speed until the mixture resembles coarse sand.
In a measuring jug, mix together the milk, egg whites, lemon zest and rosewater.
Add the egg white mixture into the batter, in three stages, mixing well on low speed after each addition. Increase the speed and mix for a couple of minutes until batter is smooth.
Divide the batter between the cake tins and bake for 35-40 minutes or until the cakes are risen and coming away from the edges of the tin. A skewer inserted in the centre should come out clean.
Cool in the tins for 10 minutes before turning out onto a wire rack to cool completely before filling.
Whisk the cold cream, icing sugar and vanilla extract until you have soft peaks.
Meanwhile, sprinkle one sachet of gelatine powder over 2 tbsp of hot water. Stir to dissolve and then microwave for 10-20 seconds until it is liquid. Add the hot gelatine into the cream once it reaches soft peaks and continue to whisk until you have firm peaks. Don’t over whip the cream or it might curdle. Put the whipped cream in the fridge for 20 minutes before using.
Position your bottom cake layer on a platter or stand and pipe generous rosettes of cream over it.
Scatter halved strawberries over the cream and then even out with more cream if needed. Drizzle with a little of the strawberry rose syrup.
Sandwich with the second layer. You can pipe any extra cream over the top layer if you like and decorate with more strawberries. Alternatively dust with icing sugar and/or decorate with fresh unsprayed roses or rose petals.
This cake is best eaten on the day it is assembled but will keep in the fridge for another day.
You can also use two 23cm (9in), three 20cm (8in), or four 15cm (6in) cake tins but you will need to adjust the baking time to 23-25 minutes.
The cake can be made a day or two in advance and kept at room temperature wrapped well with cling film.