Heat half the olive oil and sauté the onion, scallions or leek until soft and lightly golden. Add the spinach and cook until wilted. Remove the mixture with a slotted spoon and drain well in a colander. Cool.

Combine the spinach mixture with the fresh herbs. Season to taste with salt, pepper and nutmeg, Mix in the feta.

Spread the mixture onto 4 1/4-inch-thick slices of good bread. Place the remaining four slices of bread on top.

Heat a cast-iron or nonstick frying pan and add the butter or olive oil (you can use both. together). Add the sandwiches, one or two at a time, and cook over medium heat on until golden on one side. Flip carefully to cook on the other side, pressing down with a spatula. Cover the pan for a few minutes to help the feta melt more easily. Repeat with remaining sandwiches, replenishing the olive oil and/or butter as needed.