Wash the potatoes and cook in boiling salted water for 20 minutes. Cook eggs in boiling water for eight minutes, rinse with cold water, peel and halve. Heat the fat in a pot, sauté the flour in it, deglaze with stock and cream and bring to the boil.
Stir in mustard, season with salt and pepper. Wash the rocket, dab dry and cut into strips. Wash chives, dab dry and cut into small rolls. Add the rocket and half of the chives to the sauce.
Put the eggs in the sauce. Roast the mustard seeds in a dry pan. Drain and rinse the potatoes, remove the skin and press them through a potato ricer. Serve the egg ragout and the potatoes sprinkled with the remaining chives.