1. For the jelly, heat all of the ingredients (except the agar agar) until just boiling. Turn the heat off and whisk in the agar agar or add the vegetarian gelatine according to the packet instructions. Place in a greased wide, flat pan and allow to cool. Refrigerate until set and ready to use.
2. Sift together the flour, skimmed milk powder, baking powder and bicarbonate of soda. Set aside.
3. In a separate bowl cream together the sugar, lemon, sour cream and oil.
4. Gently mix in half of the sifted flour mixture.
5. Add the soda water and mix until there are not any lumps (but don’t overwork it).
6. Add remaining sifted flour mixture and then fold in using a metal spoon. Take care not to beat it too much.
7. Grease and line a 6X8inch cake tin and pile in the cake mixture.
8. Bake in a preheated oven at 160°C for 25-30 minutes. Do not open the oven door for the first 15-20 minutes of baking.
9. When cooked (insert a skewer into the centre of the cake to see if it comes out clean), remove from the oven and allow to cool on a wire rack.
10. When cool, cut into two equally sized rectangles (lengthways) as one will go on top of the other. Trim if necessary.
11. For the rose cream, whip together all of the ingredients until it reaches soft peaks.
12. Gently melt the white chocolate over a double boiler and set aside.
13. To assemble, pile the rose cream on top of one cooled sponge and top with the other sponge. If you have any leftover rose cream, why not combine it with cake crumbs and make these cute rose truffles?
14. Cut a fitting size of rose jelly to top the cake log and gently place on top. I wish mine had been neater.
15. Cover the entire cake log in half of the white chocolate. Put in the fridge to set, then repeat. This is so, SO messy. I had white chocolate in my hair, on my clothes and all over the kitchen.
16. Cover with a cascade of fresh rose petals and serve.