Line a 12-hole muffin tray with muffin cases. Put the butter and sugar into a mixing bowl and beat with an electric whisk until fluffy and creamy. Gradually add the eggs, then mix in the flour and peaches. Divide the mixture between the muffin cases and bake for 18-20 minutes or until the cakes are cooked through, golden and risen. Allow to cool.
Meanwhile, make the icing. Beat the butter until fluffy, add the icing sugar and mix until smooth. Add in the food colouring until you have a bright yellow.
When the cakes are completely cool, smooth the buttercream onto each until the top is completely covered and as smooth as possible. Allow to set for 5-10 minutes while you mix the remaining 5 tbsp of icing sugar with a little water until it is a piping consistency. Put into a piping bag fitted with a small nozzle and pipe two semi-circles onto the cakes so they resemble tennis balls. Serve or keep for up to a week.