Preheat the oven to 350°F (180°C).
Butter a cookie sheet (or a roll-shaped one) and line it with parchment paper. Butter the parchment paper. Set aside.

Peel, grate the potatoes, and dry them with paper towels.
Mix the eggs, mozzarella cheese, Cayenne pepper, green onions, and add the potatoes.
Season with salt and pepper to taste.

Spread the mixture onto the prepared cookie sheet and smooth the top with a spatula.
Bake for 30 minutes.

Remove the potato roll from the oven while it’s still warm and flip it onto a cutting board.
Spread Boursin garlic and herb cheese all over the surface, then top with smoked salmon slices.
Roll the mixture tightly. Cut into slices and serve immediately with a salad.