Watch How to Cook Well with Rory O'Connell at 8:30pm on Tuesday evenings on RTÉ One.

  1. Begin by making the cake.
  2. Preheat the oven to 180c. Brush 2 x 20cm cake tins with a little melted butter and line the bottom of each tin with a disc of non-stick baking paper. Dust out the lined tins with a little flour and tap the bottom to remove excess. 
  3. Place the butter in a large heavy bowl such as Pyrex or ceramic and beat with a wooden spoon until it has paled somewhat in colour. Add the caster sugar and continue to beat until light and fluffy. Beat in the eggs one at a time, beating well between each addition.
  4. Sieve the flour and baking powder together and mix well. Fold into the egg and butter mixture and fold in gently but thoroughly.
  5. Divide the batter between the prepared tins and bake for 20-25 minutes until the cakes are well risen, a rich golden colour and feel somewhat spongy to the touch. The cakes will have shrunk very slightly from the edge of the tins and a skewer inserted into the cake should be completely clean when withdrawn. 
  6. Remove from the oven and place on a wire rack, still in the tins. Allow to cool for 15 minutes, then gently remove from the tins and place paper side down on a wire rack to cool completely. 
  7. To make the marshmallow, place the gelatine in a small heatproof bowl such as Pyrex or ceramic. Do not use plastic or light metal or the gelatine will stick to it. Pour the water over the gelatine being careful not to splash it. Allow to sit and sponge for ten minutes. The gelatine will swell and literally take on a sponge like appearance.
  8. Place the bowl in a saucepan of simmering water and cook gently until the gelatine had dissolved into a clear liquid. I prefer not to stir the gelatine but allow it to melt in its own time. There should be no un-dissolved grains of gelatine still visible in the mixture. Turn the heat off under the saucepan and allow the gelatine to sit.
  9. Place the sugar and 250ml water in saucepan and stir over a low heat until the sugar has dissolved. You do not have to stir continuously, just occasionally. Increase the heat and continue to boil until it reaches 122c on a sugar thermometer. Remove from the heat and stir in the melted gelatine with a wooden spoon.
  10. Place the egg whites in the bowl of a stand mixer and whisk to a stiff but not dry peak. With the machine still running, pour the syrup down the side of the bowl on to the egg whites. The mixture will liquefy somewhat at this stage. That is fine. Continue whisking at a high speed until the mixture becomes really thick but still pourable. In my machine this takes between 10 and 15 minutes.
  11. To assemble the cake, remove the baking paper from the cakes and split each one in half horizontally. Place the first half on a wide flat plate and spoon on 2 generous tablespoons of the jam not pushing the jam tight out to the very edge, but leaving a 1cm rim around the edge of the cake. Scatter on the frozen raspberries. I tend to squash the berries between my fingers to get them to sit flat.
  12.  Drizzle 1 teaspoon of rosewater over the berries and smear with two generous tablespoons of the marshmallow, again not going quite out to the edge. Place the next layer of cake on top, firming it gently into place. 
  13. Continue as previously and place the final layer of cake on top. You will now have four layers of cake and three layers of jam, berries, rosewater and marshmallow. Spoon some of the marshmallow on top of the cake and spread it down over the edges.
  14. Continue using the marshmallow until the side and top of the cake are generously iced. If you have a little marshmallow left over, pop it into a tin lined with oiled parchment paper and dusted with a teaspoon each of icing sugar and corn flour sieved and mixed. 
  15. Place the cake in a cool place to allow the marshmallow to set, but do not refrigerate.
  16. When ready to serve, decorate the cake with organic rose petals, fresh or crystallised.
  17. Serve softly whipped cream to accompany the cake.