Preheat the Oven to 190C / Gas Mark 5 and grease two 20cm round sandwich tins.
Melt the squares of chocolate over a saucepan of hot water until it melts.
In a separate bowl, mix the cream and butter with the sugar until it is light and fluffy. Beat in the vanilla essence, then gradually add the beaten eggs, beating well each time.
Stir in the melted chocolate & the yogurt. Fold in the flour - use a metal spoon!
Divide the mixture evenly between the tins and bake for 25-30 minutes.
Make the frosting by melting the butter in a saucepan then remove from the heat. Stir in the icing sugar into the mixture with a rubber spatula until smooth then beat in the yogurt. When all is mixed together, add the fudge sauce to make a delicious fudgy frosting.
Use about a third of the mixture between the two sandwiches, then working quickly, spread the remaining frosting over the top.