Preheat the oven to 180 Celsius / 350 Fahrenheit (electric). Line the bottom of an 8-inch or 9-inch springform pan with parchment paper. Grease the sides with butter.
In a large mixing bowl, crack the eggs and beat them using an electric mixer or a food processor. Blend them until they are fluffy, pale, and have doubled in size, which should take about 2 minutes.
Add the full-fat yogurt, vanilla extract, and melted, cooled butter to the egg mixture. Blend until well-combined, ensuring there are no lumps remaining.
Next, add the dry ingredients: baking powder, almond flour, and the powdered erythritol. Blend again until a smooth batter forms.
Pour the batter into the prepared springform pan, ensuring it is evenly distributed.
Bake the cake in the preheated oven for about 30 minutes if using a 9-inch springform (or 40 minutes for an 8-inch pan). Check for doneness by inserting a knife or skewer into the center; it should come out clean.
While the cake is baking, prepare the frosting. In a small bowl, combine the mascarpone with the powdered sweetener and vanilla extract. Use a fork to stir until smooth, adding yogurt as needed to loosen the mixture.
Once the cake has cooled completely, gently spread the frosting on top, ensuring a nice even layer.
Finally, decorate with fresh blackberries or raspberries, arranging them on top of the frosting for a beautiful presentation.
