Preheat oven to 180C. Line muffin tin with 4 large cupcake cases. Mix flour, caster sugar and pinch of salt in large bowl.
Stir together butter, yoghurt, egg and vanilla, then pour into flour; beat until smooth. Spoon into cases and bake for 8mins until risen but v soft. Take tray out and poke truffle into middle of each cake, followed by a raspberry. Bake for another 12-15mins until golden. Cool on wire rack.
For frosting, melt remaining truffles in bowl over simmering water, stirring only once melted (don't worry if lumpy). Cool for few mins, then, using electric beaters, beat in soft cheese and 1tbsp icing sugar until smooth.
Put remaining berries and icing sugar in small pan, mash, then boil for 2mins until jammy. Cool, then sieve into plastic food bag, discarding seeds.
Cover cooled cakes with frosting. Snip corner off food bag, then squeeze raspberry coulis over each cake to decorate. Best iced on day of using/giving.