Wash the asparagus, cut off the woody ends. Peel the asparagus in the lower third and cut into pieces. Wash and peel the potatoes and cook in boiling salted water for about 20 minutes. Cook the asparagus in boiling salted water for about 10 minutes.
Cut the ham into strips. Heat the fat in a pot, dust with flour and sauté while stirring. Gradually add stock, bring to the boil while stirring. Stir in crème légère and add ham.
Season sauce with salt and pepper. Drain the asparagus, drain and add to the sauce. Wash parsley, dab dry, chop leaves finely. Drain the potatoes and let them steam for a short time. Turn the potatoes in the parsley.
Serve asparagus ragout with potatoes. Garnish with tarragon to taste.