Chocolate yam cake buttercream roses

Ingredients

• Ingredients for cake:
• 1 pack of chocolate sponge cake premix
• 1.5 cup of water
• 1/3 cup of olive oil
• 3 eggs

Ingredients for yam filling:

• 1 medium size yam, 250g (peel, steam until soft)
• 250ml thickening cream
• 2 tbsps sugar

Ingredients for buttercream:

• 250g, 1 stick of butter (soften)
• 3 cups of powder sugar
• 3 tbsps milk
• 1 drop of green food colouring