Preheat oven to 350 F (180 C).If you’re not using a silicone mold, grease it and line it with parchment paper.Beat the eggs with the sugar until the mixture doubles in volume and becomes pale.Add the yogurt, then the flour and baking powder, whisking regularly.Finally, add the oil and mix well until a smooth batter forms.Divide the batter into two parts: 2/3 and 1/3.In the 1/3, incorporate the cocoa, and in the 2/3, incorporate the lemon curd.In a silicone cake mold, pour 1/3 of the lemon curd batter and spread it evenly at the bottom of the mold.Add half of the cocoa batter, spreading it over the lemon curd batter, and repeat the process one more time, finishing with the lemon curd batter.Bake for 45 minutes or until a toothpick inserted into the center comes out clean.Lemon Curd:In a saucepan (don’t use aluminum, as it may give the cream a metallic taste), heat the lemon juice, zest, and about half of the sugar, and bring to a boil.In a large bowl, beat the eggs and the remaining sugar.While whisking, gradually add the hot liquid to the eggs.It’s essential to whisk constantly when adding the hot liquid to the eggs so they can warm up gradually.Return the mixture to the saucepan and place it over the heat.At this point, you must whisk constantly until the first boil appears.The temperature of the heat is not a determining factor.Usually, this recipe is made over high heat, whisking energetically. The result will be the same at moderate heat, but the cooking time will be longer.Remove from heat as soon as it starts boiling.The easiest way to incorporate the butter is to transfer the lemon cream to a container with high edges, add the butter gradually, and whisk with an immersion blender.When all the butter is added and the cream is smooth, strain it through a fine-mesh sieve or a china cap, cover it with plastic wrap placed directly on the cream, and refrigerate for at least 8 hours.