Chop peanuts finely. Sift flour into a bowl and make a well in the center. Cut butter into small pieces and arrange around the well. Add egg and nuts to the well. Knead into a pastry and wrap in plastic wrap, refrigerate for 1 hour.
Cut off tomato stems. Blanch tomatoes in hot water, rinse in cold water and peel, slice thickly.
Peel onion and cut into rings. Cut bacon into wide strips. Melt butter in a frying pan and saute onion rings and bacon for a few minutes.
Butter 8 tart pans and line with pastry, making edges all around. Prick pastry with a fork several times and bake in preheated oven at 180°C (gas 2-3; fan oven 160°F) (approximately 350°F) for about 10 minutes.
Whisk eggs with sour cream and crème fraîche, season with pepper. Spread cream mixture in tartlet shells and top with onion mixture and tomatoes. Bake for 15 minutes more. Sprinkle with chopped peanuts and serve.