Peel and wash the potatoes, cover and cook in boiling salted water for about 20 minutes. In the meantime heat up fat in a pot, dust with flour, sweat on, gradually deglaze with stock and cream while stirring.
Bring to the boil, stir in mustard, season with salt, pepper and sugar, bring to the boil again and keep warm. Cook eggs in boiling water for 7-8 minutes. Drain, quench and remove the shell. Halve eggs.
Cut cress from the bed. Stir 2/3 of the cress into the sauce. Drain the potatoes. Arrange potatoes, sauce and 1 1/2 eggs on plates, sprinkled with the remaining cress. Add the rest of the potatoes separately.