Preheat the oven to 350°F and lightly grease an 8-inch round cake pan, then line the bottom with parchment paper.

In a medium bowl, whisk the Greek yogurt and eggs together until the mixture is smooth, pale, and completely blended with no streaks.

Add the erythritol to the bowl and whisk until it fully dissolves into the yogurt and egg mixture.

Sift the corn starch, tapioca flour, or arrowroot powder over the wet ingredients, then whisk gently just until the batter is smooth and free of lumps.

Pour the batter into the prepared pan and smooth the top with a spatula so it reaches evenly to the edges.

Bake for 25 to 30 minutes, until the top is lightly golden and a toothpick inserted in the center comes out mostly clean with a few moist crumbs.

Let the cake cool in the pan on a wire rack for 10 minutes, then run a knife around the edges, remove it from the pan, and cool completely on the rack.

Before serving, top the cooled cake with fresh berries or mango, a sprinkle of lemon or orange zest, and shaved chocolate if desired; drizzle with honey, maple syrup, or dust with powdered sugar only if you do not need it fully sugar free.