Preheat oven to 350°F (180°C).

Boil the potatoes. Peel and grate cooked potatoes into a large bowl.

Peel the carrots, chop into small pieces and cook in lightly salted boiling water just until tender. As soon as the carrots are done, add peas to carrot water to thaw then drain both in a sieve and set aside.

Using the same pot, melt the butter and cook the onions and garlic in the butter on low heat until translucent. Add the onions and garlic to the potatoes. Finely chop the parsley and chives and add them to the potatoes as well. Add the sour cream and egg yolk. Add grated nutmeg, salt and pepper and stir mixture well. Season to taste. Stir in carrots and peas.

Unfold the puff pastry on a baking sheet. Place the potato filling on the pastry and shape with your hands into a long log. Fold the pastry over the filling and pinch edges to seal. Brush strudel with beaten egg yolk. Bake for 30 minutes until golden brown.