Melt butter, fry shallot with salt and sugar (just a little, for caramelization). Add flour, fry until golden brown, pour cream, add ground white pepper, a mixture of Italian herbs and simmer until the desired of thickening.
In another pan fry the shrimps and mussels in olive oil, literally 1 minute on each side. Then transfer to the sauce, stir and simmer together for another 1-2 minutes.
Serve with a wedge of lime and sprinkle with finely chopped cilantro.