Mix eggs and grated potatoes in bowl and season to taste with salt and pepper.
Heat olive oil and butter in large pan. Ladle in potato mixture in portions and press flat with spatula. Cook slowly around 2 minutes on each side until rösti is golden brown.
Remove rösti from pan and cover with slices of Vacherin Mont-d’Or AOP. Continue with the rest of the potato mixture. Garnish with parsley.