Preheat your oven to 350°F (175°C). Grease an 8-inch round cake pan and line the bottom with parchment paper.
In a large mixing bowl, whisk together the egg yolks, Greek yogurt, sugar, vegetable oil, vanilla extract, baking powder, and salt until smooth.
Sift the flour into the mixture and gently fold it in until just combined.
In a separate bowl, beat the egg whites with cream of tartar until stiff peaks form.
Carefully fold the beaten egg whites into the yogurt mixture in three additions, being gentle to maintain the fluffiness.
Pour the batter into the prepared cake pan and smooth the top.
Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.
Serve plain or with a dusting of powdered sugar or fresh fruit.