We're focused on the toppings here: fresh strawberry puree and piped whipped cream--so come to this recipe with your 10-inch white cake already baked and ready to go. Both the strawberry puree and the whipped cream are stabilized with a little gelatin, so they'll hold up for a summer dinner oustide, and so the cake can be made ahead by a day. Go for it and buy plastic piping tips at the grocery store, along with a gallon ziploc bag, for a fabulous yet truly simple-to-do look.
Hull and coarsely chop the strawberries. In a blender, pulse them until they are fully pureed. In a small saucepan, combine the puree with the sugar, rose water, and lemon juice. Bring to a boil, then reduce the heat and simmer until reduced by almost half, about 20 minutes.
Bloom the gelatin: In a small bowl filled with 1/4 cup of cool water, very slowly sprinkle the half-packet of gelatin evenly over the water, letting each sprinkle soak in water before sprinkling more over top. Once the powder has absorbed the water, heat in the microwave for 15 seconds. Stir the gelatin into the strawberry puree. This can be made ahead and refrigerated; soften in the microwave for 15 seconds before spreading on the cake.
Spread the strawberry puree over the top of the cake, leaving an inch perimeter around the edge.
Make the stabilized whipped cream when you're ready to frost the cake:
Bloom the gelatin again: In a small bowl filled with 1/4 cup of cool water, very slowly sprinkle a full packet of gelatin evenly over the water, letting each sprinkle soak in water before sprinkling more over top. Once the powder has absorbed the water, heat in the microwave for 15 seconds.
In a stand mixer or using a hand mixer, beat the cold cream with the sugar, rose water, and vanilla on high speed until it is thick and showing lines from the beater. Pour in the gelatin and continue to beat until the whipped cream is very thick and holds a stiff peak.
Using a piping bag or a gallon ziplock bag with a tiny bit of the corner cut off, put a star tip into the opening, then fill the bag with the whipped cream.
Starting at the base of the outside of the cake, pipe all the way around the cake. Do this again just above the first line, then again above the second line. Pipe stars around the perimeter of the cake on top in the area left free of strawberry puree. Top each star with alternating strawberries and blueberries.