Bring the butter and water to the boil. Put in the peas, sugar and season with salt and pepper. Simmer, covered over low heat for 8-10 minutes, until the peas are almost tender. If more than a few spoonfuls of liquid are left in the pan, leave it uncovered for the moisture to evaporate. Blend the saffron with 2 teaspoons of water and stir it into the cream with the flour. Pour the cream over the peas, as soon as the cream comes to the boil, stir in the dill or chives and serve the peas.