Combine flour, warm water, olive oil, and salt in a bowl to form a dough. Knead until smooth, then cover and let rest for 30 minutes.

Boil potatoes until tender, then mash.

In a pan, sauté onion and garlic until translucent. Add spinach and cook until wilted.

Combine mashed potatoes, sautéed spinach mixture, ricotta, salt, and pepper in a bowl to form the filling.

Divide the dough into small pieces and roll each into a circle. Place a spoonful of filling in the center of each circle.

Fold the dough over the filling to create a half-moon shape, sealing the edges by pressing them together.

Bring a large pot of salted water to a boil. Cook pirogi in batches for 3-5 minutes or until they float to the surface.

Serve hot with a dollop of sour cream and a sprinkle of fresh herbs, if desired.