Halve the fennel and cut into thin slices. Cut the celery into 1cm pieces. Sauté the fennel and celery in hot oil. Pour in the white wine and bouillon. Cover and allow to cook for around 10 minutes until crispy. Remove the vegetables from the liquid and allow to cool. Boil down the liquid to 2 tablespoons.
Peel the potatoes and cut into 2cm cubes. Cut the pork ribs lengthways.
For the sauce, mix the eggs, Gruyère AOP, cream and milk. Add the liquid, squeeze in the clove of garlic, season with mustard, salt and pepper. Finely chop the fennel and celery leaves, mix with vegetables, potatoes and pork ribs with the sauce.
Place the shortcrust pastry in a suitable baking tray. Press the pastry in firmly with a fork. Spread the filling over the pastry. Bake on the lower shelf of the oven at 220°C for around 30 minutes. Serve hot or cold.