For the pastry: Pile flour on the work surface, mix with salt and make a well the center. Cut cold butter into small pieces and arrange around the well. Add an egg to the well and chop all ingredients with the knife until crumbly.
Quickly knead into a smooth pastry with your hands, shape into a ball, wrap in plastic wrap and refrigerate for about 30 minutes.
For the topping: Peel onions and cut into thin rings. Peel garlic, squeeze through a press and combine with chopped dill and onions.
Whisk eggs with cheese and cream in a bowl and season with salt and pepper.
Roll out pastry on a floured surface and line tart pan with it, making an edge all around. Bake in preheated oven at 200°C (approximately 400°F) for about 5-10 minutes.
Remove from the oven and spread onions and egg mixture on top (if desired, sprinkle with anchovies and olives). Bake for 15-20 minutes more. Remove from the pan and serve warm.