Beat the eggs and sugar with a mixer until whitened.
Mix the flour with the cocoa, baking powder, vanilla and sift. Add this mixture gradually to the egg mixture. Pour into a greased form and bake in a preheated oven at 356°F (180 °C) for 30 min, then allow to cool.
Melt the white chocolate in a water bath. Add the strained yogurt to the chocolate, add the powdered sugar and the dissolved gelatin.
Allow the cream to harden. Beat the butter with a mixer, and to it gradually add the sugar and milk until the mixture homogenizes. Cut the cake layer in half and put the chocolate cream in between them. Smear the top and sides with the buttercream. Allow to solidify at room temperature, while you get to work on the fondant.
Dissolve the gelatin in the water for about 4-5 min. Mix the powdered sugar with the corn starch and sieve it 1-2 times. Put it in a bowl and make a well in the middle.
Pour in the gelatin in and stir with a wooden spoon until the powdered sugar is absorbed. Leave it for about 20 minutes to set. With the remaining powdered sugar, knead by hand to make a ball.
When kneaded by hand, it is soft. If left for awhile it hardens, but as soon as you knead again it becomes soft like modeling clay. If it is too dry, add a few drops of water; if it is too soft, add powdered sugar.
Roll out the fondant onto a counter sprinkled with powdered sugar (tablecloth). Spread it over the cake on the top and sides, pressing with a spatula to prevent any air from remaining between the cake and fondant.
Cut off the parts that stick outside the cake with a sharp knife, separate them into balls and color them with different dyes. Put a little dye (dry or wet) in each ball and knead until a you get a uniform color. Use your imagination to make figurines and while they are still soft, decorate the cake with them.
You can store any leftovers in transparent foil in the refrigerator for quite a long time. Bon appetit!
PS: With the white chocolate on inside, the aesthetic effect is even better. I decided to try it with cream cheese instead of yogurt.