Dissolve seasoned stock base in water and pour over potatoes which have been quartered. Bring to a boil then simmer 20 minutes or until tender. Drain; cut into cubes and pace in a buttered 1.5quart baking dish. Melt the 3 tablespoons butter in a saucepan; stir in arrowroot, salt, pepper, season all, dry mustard and nutmeg. Add milk and cook over medium heat, stirring constantly, until smooth and thickened. Stir in 1 cup of the cheese and continue cooking until cheese melts. Pour over potatoes. Toss bread crumbs with the 2 tablespoons melted butter; spoon evenly over all. Top with the remaining cheese and sprinkle generously with the paprika.