Frankfurt Green Sauce with Potatoes

From the garden

• 4 cups soft herbs (parsley, chives, and dill), packed, thick stems pulled off · parsley and chives should make up at least half the pile
• 1 cup sorrel leaves, packed (optional) · the classic sour note; without it, lean harder on the lemon
• ½ cup fresh chervil, packed (optional)
• ½ cup garden cress, packed (optional) · watercress, or a handful of young radish tops, gives the same peppery lift
• 2 lb small waxy potatoes, scrubbed, halved if bigger than a walnut

From the pantry

• 8 eggs · six go on the plate, two are mashed into the sauce
• 1 cup sour cream
• ¾ cup plain Greek yogurt · quark is traditional; yogurt and sour cream together land in the same place
• 2 tsp Dijon mustard
• 3 tbsp olive oil
• 1 lemon, juiced
• 1 pinch sugar
• salt · to taste
• black pepper

1. Boil the potatoes in well-salted water until a knife slides in with no resistance, 15–20 minutes depending on size. Drain and leave them in the warm pot with the lid ajar to steam dry.
2. Lower the eggs into a second pan of boiling water and simmer 9 minutes for firm yolks, then cool them under cold running water and peel. Set six aside whole for the plate.
3. Wash and dry the herbs thoroughly, then chop them fine by hand in loose batches. A blender is faster but bruises the leaves and can push the sauce toward bitterness.
4. Mash the yolks of the two remaining eggs with the mustard, then whisk in the olive oil a spoonful at a time. Fold in the sour cream, yogurt, lemon juice, and sugar until smooth.
5. Chop those two egg whites fine and stir them in with all the herbs. Season hard with salt and pepper, since cold dairy swallows salt and this should taste sharp straight off the spoon.
6. Chill the sauce 30 minutes so the herbs bleed into it, then halve the reserved eggs and serve them with the warm potatoes under a generous blanket of green sauce.