Heat the oven to 220°C (425°F, gas mark 7). Heat the oil in a large saucepan, then add the rabbit and bacon. Cook, stirring, until golden.
Add the onion and garlic and cook for 1-2 minutes. Stir in the carrots, wine, stock, lentils, thyme, bay leaf, vinegar, salt and pepper.
Bring to the boil, reduce the heat, cover and simmer gently for 20 minutes. Meanwhile, sift the flour into a bowl, add the celery salt and rub in the butter. Stir in the chives and milk. Mix to a firm dough. Knead gently, then roll out on a lightly floured surface to 1cm (½ in) thick and stamp out 20 rounds.
Add the mustard to the rabbit and spoon the mixture into an ovenproof dish.
Put the rounds over the rabbit and brush with milk. Bake for 15-20 minutes, until golden brown.