How do I ice Nigella's birthday number biscuits

[DollyDaisy]

I'm sure this is a really silly question, but how exactly do I ice the coloured block areas on Nigella's birthday number biscuits?

I dont think the icing pens will work as they will be too fine. And I don't think the picture in the recipe book looks like rolled icing. So do I need to do it with a paint brush or something??

Thanks in advance

Couldn't you just use normal icing? I.e made with icing sugar and water. You can flavour with lemon juice or cocoa powder if you like. This sort of icing is really easy, and quite a good consistency for icing biscuits I'd have thought?

OK thanks for this. So apart from icing a thicker line first then filling in with watered down icing, I could just potentially dollop on some normal icing and then spread it into shape with a teaspoon??? All the recipes just say "ice the biscuits"...but I don't know how!

I'm actually quite embarrassed to be typing this.....I really enjoy cooking and think I'm quite good at it, but this is my first foray into children's parties and making this sort of thing