Put the yogurt into a cheesecloth and allow it to drain. Thoroughly wash and peel the oranges. Grate half the rind. Crumble the biscuits and mix them with the melted butter and orange zest. Pour the resulting mixture into a cake form and leave it in the refrigerator for 1 hour.
Mix the strained yogurt with the sugar and a small part of the orange zest. Blend everything until you get a smooth mixture. Distribute it onto the now tightened layer.
Top with bits of orange. Put it back in the refrigerator for several hours and then release it from the form to cut the cake into pieces and serve it.