In a bowl, combine the cream and mustard. Add the celery root and stir to combine. Season with salt and pepper. Let rest for 15 minutes.
Toast the bread slices. Spread with mayonnaise and Dijon mustard to taste. Cover 4 bread slices with the roast beef and remoulade salad, then top with the tomato slices and lettuce. Close each sandwich with a second slice of bread and serve.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.