Heat the milk in a saucepan and bring to the boil briefly. Add rice pudding, cover and cook over low heat for about 45 minutes. Clean, wash and cut the rhubarb into pieces of about 1.5 cm width. Put 100 ml maple syrup into a pot and cook on low heat for 5-8 minutes until the rhubarb is soft but not yet decomposed.
Place the rhubarb in 2 small (750 ml capacity each) or 1 large (1.5 litre capacity) casserole dish. Stir 75 ml maple syrup into the rice pudding. Separate the egg. Beat egg white and salt until stiff, whisk egg yolk and cream, stir into the rice pudding.
Fold in the beaten egg white and carefully spread on the rhubarb. Sprinkle with the flakes. Bake in the preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: level 4) for 4-5 minutes. Sprinkle with maple syrup.
Serve decorated with mint.