For the frittata, peel, wash and dice the potatoes and cook in salted boiling water for 10 minutes. Just before the end of the cooking time, add the peas. Drain everything, chill it cold and drain well.
Preheat the oven to 190 ° (convection 170 °). Peel and finely dice the shallots. Beat eggs in a bowl; Stir in the créme fraîche and mustard. Coarsely grate the cheese.
Heat the olive oil in a large, ovenproof pan, fry the diced potatoes, peas and diced shallots in it over a medium heat for about 2 minutes. Season with salt and pepper. Pour the egg crème fraîche mixture over it and let the frittata bake for approx. 4 minutes (do not stir). Sprinkle the frittata with the grated cheese and finish cooking in the preheated oven in about 12 minutes.
For the dip, cut the chives into small rolls. Mix the quark with the chives, cream and cayenne pepper. Season to taste with salt. Take the frittata out of the oven and let rest for about 2 minutes. Slide onto a platter, cut into pieces and serve with the chive dip.