Preheat oven to 150°C (300°F) and line a baking tray with greaseproof paper.

Separate eggs into yolks and whites.

In a bowl, whisk egg yolks, cream cheese (or mascarpone), and salt until creamy and smooth.

In a separate bowl, whisk egg whites and cream of tartar until stiff peaks form.

Gently fold the whipped egg whites into the yolk mixture in stages, rotating the bowl to maintain volume.

Spoon 6 dollops of the mixture onto the prepared baking tray.

Slightly flatten the dollops with an egg spatula.

Bake for approximately 30 minutes, or until golden brown.

Let cool for a few minutes on the baking tray before transferring to a wire rack to cool completely.

Butter the flat sides of the rolls.

Use the rolls to make sandwiches.