1.Place garlic in small saucepan, cover with cold water; bring to the boil, drain.
2.Meanwhile, place mustard seeds in small dry frying pan; cook over medium heat until seeds begin to pop.
3.Crush garlic into medium bowl. Add seeds, cornichons, celeriac, parsley, mayonnaise, mustard and juice; mix well. Season to taste.
4.Split bread sticks in half through the top, without cutting all the way through; fill with beef and remoulade. Wrap roll securely in baking paper or lunch wrap.
If you don’t have any leftover roast beef, buy thinly sliced cold roast beef from the delicatessen. You could replace the beef with barbecued chicken. You need about a quarter of an average celeriac. Celeriac discolours quickly once cut, so use it straight away or place in a bowl of cold water with lemon juice added.