Preheat and Prepare: Adjust your oven rack to the middle position and preheat to 300°F (150°C). Line a large baking sheet with parchment paper. Lightly greasing the parchment is optional but can help prevent sticking.

Whip Egg Whites: In a large, impeccably clean bowl, beat the egg whites using an electric mixer on high speed. Continue until stiff peaks form – the peaks should stand straight up when you lift the beaters.

Mix Yolk Base: In a separate medium bowl, combine the softened mascarpone cheese, egg yolks, sea salt, and optional vanilla extract. Beat with the electric mixer (ensure beaters are clean) on low to medium speed until the mixture is completely smooth and evenly blended.

Combine Gently: Add approximately one-third of the whipped egg whites to the yolk mixture. Use a spatula to gently fold them in until just combined. Add the remaining whites in two more batches, folding carefully after each addition. Be careful not to overmix; stop folding when there are no large streaks of white visible, preserving as much air as possible.

Shape the Rounds: Carefully spoon or scoop the batter onto the prepared baking sheet, forming 8 separate circular mounds. Allow some space between each mound for potential spreading.

Bake: Place the baking sheet in the preheated oven. Bake for 25 to 35 minutes, or until the cloud bread rounds are puffed, appear set, and are a light golden-brown color.

Cool: Remove the baking sheet from the oven. Let the cloud bread rounds cool on the sheet for 5-10 minutes (they might deflate slightly). Then, carefully transfer them to a wire rack to cool completely before serving.