Preheat oven to 180 degrees celcius. Make the mayonnaise.Heat the olive oil in a tray and add the potatoes and the thyme.Season and place in the oven for 20 to 25 mins, turning once or twice.Place the onions in a pan with the butter and some more thyme. Cook very slowly with a lid for 20 mins until the onions are totally soft. Season and set aside.Heat a frying pan. Add a little oil and cook the lamb chops for 4 mins on either side to be pink or more if you like.Season and serve with the onions, potatoes, mayonnaise and wild garlic pesto.

To make the mayonnaise Place the egg yolks in a bowl with a pinch of salt, mustard and some vinegar. Beat well with wooden spoon.Add the oil, drop by drop, beating all the time, ensuring mixture is thickening before adding the next drop. The mixture should be very thick by time half the oil is added. Beat in the lemon juice.Resume pouring in the oil and alternate with small dribbles of remaining vinegar. When finished, fold in the crème fraiche. Season to taste with salt and pepper.