Preheat oven (electric cooker: 200 degrees/circulating air: 175 degrees/gas: see manufacturer). Separate eggs for the dough. Cream 150g butter, 2 tablespoons sugar and egg yolk with the whisk of the hand mixer for about 4 minutes.
Beat the egg whites until stiff, then pour in 100g of sugar. Mix flour, almonds, baking powder and cocoa, stir briefly into the butter-egg yolk mixture. Fold in the beaten egg white.
Place paper cups in a muffin baking tray (12 trays). Spread the dough inside. Place 1 ball of "Rondnoir" on each and press in lightly. Bake in a hot oven for about 20 minutes.
Let cupcakes rest in the mould for about 10 minutes, then take them out and let them cool down.
For the buttercream, whisk 175g butter and icing sugar with the whisk of the hand mixer until foamy. Stir in the yoghurt bit by bit. Colour the cream yellow with a little turmeric or yellow food colouring.
Pour into a piping bag with perforated nozzle or star nozzle. Spray 2 rows of petals around each chocolate ball.